Twenty-one metres, and the drawing acquires a shaft
A seven-storey block, top floor level at 21 m above the road. Everything below that height was a fire strategy made of stairs, doors and compartment floors, priced by people who build stairs, doors and compartment floors. Cross 18 m and the drawing acquires a firefighting shaft: a stair, a lobby, a firefighting lift and a fire main, all inside one protected enclosure, all of which have to be right at frame stage because not one of them can be threaded in afterwards.
The main is the cheapest thing in that shaft and the item most often left unassigned. It is not the sprinkler subcontractor's, because it feeds nothing they install. It is not the plumber's, because it carries no potable water and answers to a different set of documents. On a good job it belongs to a fire systems contractor with the builder's work packaged around it; on a bad one it turns up as a line in a mechanical schedule three months after the shaft walls closed, at which point the inlet has nowhere to go and the outlets are on the wrong side of a door.
Three decisions do most of the work, and they come in a fixed order because each constrains the next. Whether the main can stay empty until the brigade fills it, or has to be permanently charged. Where the inlet goes, which is a site layout question about where an appliance can stand rather than a plumbing one. And where the outlets go, which is a hose-reach question about the floor plate. Get those three right and the rest is pipe.
Two thresholds, and neither of them is about how big the fire is
The triggers are geometric, not risk-assessed. In England, Approved Document B, Volume 2 puts firefighting shafts into buildings with a floor more than 18 m above fire service vehicle access level, or more than 10 m below it, and puts a fire main in the shaft. The same document sends you from a dry main to a wet one where a floor sits more than 50 m above that access level. In the United States the International Building Code asks for standpipes where the floor level of the highest storey is more than 30 ft above the lowest level of fire department vehicle access, or the lowest storey is more than 30 ft below the highest level of access, with the high-rise provisions of the code beginning at 75 ft.
The 50 m line is arithmetic wearing a regulation. Fifty metres of water is 4.90 bar, or 71 psi, and that is the tax the pipe collects before a drop of it moves. Add the running pressure the topmost landing valve has to see for a branch to throw a usable jet, add whatever the bore takes in friction, and the figure the brigade's appliance pump has to produce at ground level walks up towards the top of what an appliance pump produces at all. Above 50 m you are asking for something that cannot be reliably delivered from a hose reel and a hard standing, so the water has to already be up there.
North American practice splits the same decision on a second axis that does not appear in the British documents at all: temperature. NFPA 14 names five system types — automatic wet, automatic dry, semiautomatic dry, manual wet and manual dry — and an unheated parking deck, an open stair or a building shut down for a Minnesota winter makes a charged main a burst pipe waiting for February. A dry or semiautomatic dry system with supervisory air and a deluge valve at the base answers a freezing problem, and has nothing whatever to do with how tall the building is. Read the two axes separately, because a building can be tall enough to want wet and cold enough to forbid it, and that combination is what heat-traced and dry-pipe standpipe designs exist for.
| Trigger | England, Approved Document B Vol 2 | United States, IBC and NFPA 14 |
|---|---|---|
| Fire main becomes necessary | A floor more than 18 m above access level | Highest storey floor more than 30 ft above the lowest access level |
| Deep basements | A floor more than 10 m below access level | Lowest storey more than 30 ft below the highest access level |
| Main must be permanently charged | A floor more than 50 m above access level | System type chosen by occupancy, height and freezing risk |
| Outlet size at the landing | 65 mm instantaneous landing valve | 2½ in Class I, 1½ in Class II, both for Class III |
| Where the outlets live | Protected stairway or firefighting lobby | Each intermediate landing of every required exit stairway |
Put in the vertical distance from the inlet to the highest landing valve and read what the building costs you before any water moves. This one number decides dry against wet, and it is the number most often argued about in a pressure unit that hides how big it is.
The vertical height of the water column, in feet.
Static pressure
43.35 psi
1 ft of water at 4 °C = 62.428 lb/ft³ ÷ 144 in²/ft² ≈ 0.4335 psi. Equivalently, 2.31 ft per psi. Assumes clean water at 4 °C. For any other fluid, multiply by its specific gravity.
- Head entered
- 100 ft
- Pressure
- 43.35 psi
- Metric equivalent
- 43.35 psi
- Bar
- 2.99 bar
They open the calculator with your figures already in it
Feet of Head to PSI Calculator: 43.35 psi — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 43.35 psi — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- This is static head only. Friction loss through pipe, fittings, valves and the meter, and the residual pressure a fixture, shower or sprinkler head needs to work, are all excluded. Total dynamic head is static head plus those two, and sizing a pump on this figure alone is how a system ends up short at the top outlet.
- The factor assumes clean water at 4 °C and the result does not scale for any other fluid. Glycol, brine, fuel oil and hot circulating water all differ in density, so multiply by specific gravity yourself — a strong glycol charge reads low here, hot heating water reads high.
- It describes a column at rest. Velocity head, a pump running near shut-off, thermal expansion in a closed circuit and water hammer on valve closure can all push real system pressure well above this figure, and it is the peak, not the static value, that splits a fitting or lifts a relief valve.
- Only the water column's own pressure is counted. Fill pressure in a sealed heating circuit, an expansion vessel's charge, a booster set's outlet pressure or gas pressure above the water in a closed tank all add on top of this number and none of them are in it.
- This is not a pressure rating check and not a pump selection. It says nothing about the pressure class of the pipe, fittings, cylinder or appliance at the bottom of the lift, and nothing about NPSH available at a pump suction — cavitation is governed by suction conditions, not by the discharge head being converted here.
Pumps are catalogued in feet of head; gauges and fixtures are rated in psi. Converting between them is the moment a pump curve becomes a check you can carry out with a gauge, and it is where a system that looked adequate on paper turns out to be 15 psi short at the top floor.
Six parts, six different people, one handover
Drawn as a whole, a rising main is short on components and long on interfaces. It is a vertical pipe with a way in at the bottom, a way out at every floor, a way of releasing the air it displaces at the top, something holding it to the building, and — if it is wet — a pump and a stored volume at the foot. Six items. On site those six are bought under four packages and installed across eight months, and the defect list at handover is almost always one of them: the drain nobody piped to a gully, the air valve left off because the ceiling closed first, the inlet box that arrived after the render.
The drawing below is worth walking through with the programme open, because the sequence matters more than the specification. The riser and its supports go in with the frame. The landing valves go in when the shaft walls close and are then damaged by everyone else's works. The inlet box is a builder's work opening in an external wall and has to be coordinated with the cavity, the lintel and the cavity barrier. And the plant, if there is any, occupies the corner of the basement that the parking layout wants.
A fire main from the breeching to the head of the riser
- Air release valve and head of the main — lets the air out as the main charges and back in as it drains, and is the item that gets omitted because the shaft ceiling closes before anyone reaches it Pipe Volume Calculator
- Landing valves, one on every floor — sited inside the protected stair or firefighting lobby, and positioned so a charged hose can actually be coupled with the door swinging clear PSI to Feet of Head Calculator
- Riser clamps and firestopped floor penetrations — each clamp carries the steel and the water above it, and each penetration is a tested seal through a compartment floor rather than a hole with foam in it Pipe Hanger Spacing Calculator
- The rising main — galvanized or black steel at 100 mm or 150 mm nominal bore, sized on simultaneous outlets rather than on saving head Domestic Water Pipe Friction Loss Calculator (Hazen-Williams)
- Wet riser pump set and suction tank — duty and standby pumps on a stored volume, in a rated enclosure with its own power supply and its own drainage Hydronic Circulator Pump Head Loss Calculator
- Fire service inlet breeching — two-way or four-way instantaneous couplings in a marked box, within reach of the appliance hard standing and visible from it Feet of Head to PSI Calculator
The inlet is a site layout decision, taken far too late
An inlet breeching is a box in a wall with two or four instantaneous couplings behind a door. What makes it difficult is that its position is fixed by something outside the building: the hard standing an appliance can occupy while pumping. BS 9990 wants the inlet close to that standing — within 18 m of it — and visible from it, on the same elevation as the shaft it serves, so a crew arriving at night can find it without walking the perimeter. That is a constraint on landscaping, on parking, on the bin store, on the substation, and on whatever the planner has asked for along the frontage. It belongs in the site layout review, not in the mechanical coordination meeting.
The pairing between bore and breeching is fixed and worth knowing before the box is ordered: a 100 mm dry main takes a two-way inlet, a 150 mm main takes a four-way, and the couplings are 65 mm instantaneous. Behind the box sits a wheel-operated valve and a drain, and that drain is the detail that gets missed. After a main has been used it is full, and a 150 mm riser 60 m tall holds well over a cubic metre of water. If the base of the main does not fall to a gully, that water leaves through the lowest thing that will open, which is usually the lobby floor.
Then there is the wall the box goes in. It is a builder's work opening in an external envelope, so it carries a lintel, a cavity closure, a cavity barrier where one is required, a weather seal and — if the wall is insulated — a cold bridge that has to be detailed rather than discovered. Ordering the box late means cutting that opening after the render, and a cut opening in a rendered cavity wall is a repair, not a detail. Inlets are also stolen for their brass, jammed open, and used as bins; a padlocked door with a frangible strap and a six-monthly look inside is the whole of the maintenance regime, and it is worth writing into the operation and maintenance manual rather than assuming.
Landing valves, and the floors where pressure is the problem
Outlet position is a hose-reach question about the floor plate, and the two codes ask it differently. Approved Document B puts the outlet inside the protected stairway or the firefighting lobby and limits how far a crew has to run hose from it across the storey. The IBC is more explicit about the count: hose connections at every intermediate floor landing of every required exit stairway, at the highest landing where a stair gives roof access, on each side of a horizontal exit, and then extra connections wherever the most remote part of a floor is more than 150 ft from one in an unsprinklered building or more than 200 ft in a sprinklered one. On a deep floor plate that last clause is what puts an outlet somewhere other than the stair.
Class is the other half of the specification and it is a decision about who uses the outlet. A Class I system gives the fire service a 2½ in connection and nothing else. Class II gives occupants a 1½ in connection with hose. Class III gives both. British practice separates the two functions entirely — 65 mm landing valves for the brigade on the rising main, hose reels as a separate installation to their own standard — and importing an American schedule without noticing produces outlets nobody in the building is trained or permitted to use.
The pressure problem on a tall main is the opposite of the one plumbers are used to. NFPA 14 wants 100 psi residual at the outlet of the hydraulically most remote 2½ in connection while the system is flowing its demand, which is easy to state and expensive to provide. But hold that at the top of a 100 m main and the static pressure at the outlets near the bottom is the same 100 psi plus everything the column adds, and the code caps a hose connection at 175 psi before a pressure-regulating device becomes mandatory. Seventy-five psi of headroom is 173 ft, or 52.7 m: every landing valve more than about fifty metres below the top of a single zone needs regulating, and on a genuinely tall building that is most of them.
Pressure-regulating landing valves are not interchangeable with plain ones and they are not a field adjustment. They are selected on inlet pressure, outlet pressure and flow from the manufacturer's own curves, they are set and labelled at a specific floor, and they get swapped during a refit by someone who saw a valve and bought a valve. Recording the setting on the valve, on the record drawing and in the manual is five minutes that survives the building.
| Class | Outlet | Intended user | Residual at the remote outlet |
|---|---|---|---|
| Class I | 2½ in hose connection | Fire service, with their own hose and branch | 100 psi |
| Class II | 1½ in hose connection with hose | Trained occupants, first aid firefighting | 65 psi |
| Class III | Both sizes at the same location | Either, from one riser | 100 psi at the 2½ in outlet |
| UK equivalent | 65 mm instantaneous landing valve | Fire service only; hose reels are a separate system | Set by BS 9990, not by this table |
Enter the difference between the pressure you are holding at the top outlet and the maximum a hose connection is allowed to see, and the answer is the vertical distance below the top at which pressure-regulating valves start. Everything below that line is a different valve with a different price and a different commissioning record.
The water pressure in PSI.
Equivalent feet of head
115.3 ft of head
They open the calculator with your figures already in it
PSI to Feet of Head Calculator: 115 ft of head — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- Head is counted from wherever the gauge is, not from the ground. A basement tank reading 50 psi converts to 115 ft, but a fixture 25 ft above that gauge has already spent 10.8 psi of it before a tap opens and sits at about 39 psi at rest. Read the pressure and the point you care about as a pair, or the converted figure describes a place nobody is showering in.
- A well or booster system does not hold one pressure, so a single converted figure describes one moment of the cycle. A 40/60 switch runs everything between 92 and 138 ft of head, and a sprinkler zone or top-floor shower that performs at cut-out can fade badly just before the pump restarts. Convert the cut-in pressure, not the cut-out one, when what you want is the worst the system will do.
Bore, and the one water job where friction is the small number
Every instinct built up on domestic pipework misleads here. On a house, static lift is trivial and friction in a long thin pipe is the whole complaint — the ground the shower guide covers in detail for a mixer valve on a gravity supply. On a rising main the relationship inverts. A 110 m run of 150 mm steel flowing 500 gpm loses about 2.5 m of head to friction. The same 100 m of height costs 100 m of head before anything moves. Friction is under three per cent of the duty, and no amount of upsizing meaningfully changes the pump you need.
So bore is chosen for other reasons: how many outlets have to run at once, what velocity you are willing to live with, and the pairing the code sets with the inlet. The table below is a 110 m equivalent length — a 100 m riser plus the horizontal at the base and an allowance for fittings — at a Hazen-Williams C of 120, which is NFPA 13's coefficient for galvanized steel. Black steel in a dry system takes C of 100 in the same table, and a dry main is exactly the pipe that earns the lower figure: it is wetted, drained and then left standing full of damp air, year after year, which is a corrosion regime rather than a pipe condition.
Read the velocity column rather than the head column. A 100 mm main asked for 750 gpm is moving water at 5.8 m/s, which is where a landing valve slammed shut stops being a valve operation and starts being a shock loading on every joint and clamp in the shaft. The head loss at that flow is 39 m, which sounds survivable next to a 100 m lift and is not the reason to go up a size. The velocity is.
| Bore | At 1,500 L/min | At 500 gpm (1,893 L/min) | At 750 gpm (2,839 L/min) | Velocity at 500 gpm |
|---|---|---|---|---|
| 100 mm nominal, 102.3 mm bore | 11.9 m | 18.3 m | 38.7 m | 3.84 m/s |
| 150 mm nominal, 154.1 mm bore | 1.6 m | 2.5 m | 5.3 m | 1.69 m/s |
| 200 mm nominal, 202.7 mm bore | 0.4 m | 0.7 m | 1.4 m | 0.98 m/s |
Run your own riser with the real bore rather than the nominal size, the length including the horizontal at the base, and a C of 120 for galvanized steel or 100 for black steel in a dry system. Straight pipe only — the bends at the base and every landing valve tee are added separately as equivalent length.
The total length of the pipe run.
The design flow rate through the pipe.
The pipe material's Hazen-Williams roughness coefficient.
The pipe's actual internal (bore) diameter.
Friction head loss
17.96 ft
They open the calculator with your figures already in it
Domestic Water Pipe Friction Loss Calculator (Hazen-Williams): 17.96 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
What this calculation does not cover
- Hazen-Williams is an empirical fit to cold water in turbulent flow, roughly 40 to 75 °F (4 to 24 °C) at velocities in the 2 to 10 ft/s (0.6 to 3 m/s) band. Outside that it drifts: glycol-charged loops, hot recirculating mains and low-flow trickles are Darcy-Weisbach problems, where viscosity enters the calculation instead of being absorbed into a single C value. The formula still returns a number for any of them; it is just not the loss you will measure.
- Head loss is one term of the pressure the fixture actually sees. What is available is the incoming main, less the static lift to the outlet, less this friction, less the fittings, and less every device in the line — a meter, a backflow preventer, a filter and a softener can take 20 to 30 psi (207 kPa) between them. A run whose friction loss looks comfortable here can still open at a shower with nothing left.
- Velocity is not reported, and velocity is often what sizes the pipe rather than head loss. Copper is normally held near 8 ft/s cold and 5 ft/s or less on hot recirculating lines, because water moving faster erodes the inside of elbows and tees over the years and makes the pipe audible in the wall. A small pipe on a short run can pass a friction check comfortably and still be the wrong size.
What the wet option actually drags into the basement
Once the main has to be permanently charged, the pipe stops being the job. Take the 100 m building above: 100 m of static lift, 2.5 m of friction over the equivalent length, and 70.3 m of residual to hold 100 psi at the topmost outlet. That is 173 m of total head, which is 246 psi, or about 17 bar, at 500 gpm. A pump that does that is not a plant item you slot into a cupboard.
NFPA 20 then constrains the shape of its curve, and the constraint has a consequence people miss. The pump must deliver rated flow at rated pressure, must still hold at least 65 per cent of rated pressure at 150 per cent of rated flow, and must not exceed 140 per cent of rated pressure at churn. Take 140 per cent of that 246 psi and you get 344 psi at shut-off, against the 350 psi maximum system working pressure NFPA 14 allows. The building above is at the ceiling of what a single-zone standpipe can be built from, and it got there on height alone.
The stored volume is the item that eats floor area. NFPA 14 asks the water supply to sustain the system demand for 30 minutes. At 500 gpm that is 15,000 US gallons, or 56.8 m³. At the 1,000 gpm demand a fully sprinklered building with more than one riser reaches, it is 30,000 gallons — 113.6 m³, and about 113 tonnes standing on a slab that has to be designed for it. The metric equivalent lands in the same place: 1,500 L/min for half an hour is 45 m³. BS 9990 sets the stored volume and the assured infill rate for a wet riser in the UK, and an infill credit is what keeps these tanks from being larger still, but the arithmetic is always flow times duration and the answer is always a room.
Power is the third item, and it is the one that turns a mechanical package into an electrical one. NFPA 20 wants a reliable supply for an electric fire pump, which in practice means a second utility feed, an on-site generator, or a diesel-driven pump instead; NFPA 70 Article 695 governs how the circuit is run and protected, and it is deliberately unlike every other circuit in the building. Choose diesel and the fuel storage follows the standard's own rule of a gallon per horsepower plus allowances for expansion and sump, plus a flue, plus combustion air, plus a fuel delivery route somebody has to reach.
Add the jockey pump that stops the main cycling on a weeping valve, the test header and flow meter that the annual test needs, the drainage for a full-flow test, and the fire-resistance-rated separation NFPA 20 requires around the pump room, and the plant occupies a serviceable, drained, ventilated, rated room with vehicular access to it. That room is at the bottom of the building, which is exactly where the developer drew car parking. Establishing its footprint before the basement is set out is the single most valuable thing this decision produces.
This scales a friction rate by the total equivalent length and does nothing else, which is precisely the friction step of the duty above — the label says hydronic circulator, the arithmetic is the one a fire pump schedule uses. The static lift and the residual at the top outlet are yours to add afterwards, and on a rising main they are the large half.
The friction head loss per 100 ft (or 100 m) of pipe run, from a pipe sizing chart or a Hazen-Williams friction loss calculation at the design flow rate.
The straight pipe length plus the equivalent length of all fittings, valves, and equipment in the circuit's index (longest/most-resistant) run.
Total pump head required
10 head units
Friction loss rate must come from your system's actual pipe sizing chart or Hazen-Williams calculation for the design flow rate — this calculator only scales that rate by total equivalent length; it does not calculate the friction loss rate itself.
They open the calculator with your figures already in it
Hydronic Circulator Pump Head Loss Calculator: 10 head units — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- Head on its own selects no circulator. A pump is chosen where the required head and the design flow meet on its curve, so this figure has to be carried forward with the same flow rate the friction loss rate was read at — two systems needing identical head at very different flows take entirely different pumps.
- Plain water is assumed. A 30 to 50 percent propylene glycol charge is thicker and heavier, raising circuit friction at the same flow and cutting the flow any given pump delivers, so a snowmelt slab or a freeze-protected loop sized from a water friction rate ends up short of flow at the far end of the circuit.
- In a closed loop the pump lifts nothing — the down-leg balances the up-leg — so building height belongs nowhere in this figure and adding it oversizes the pump. The reverse applies to an open circuit such as a drainback array or an open tank: there the vertical rise from the water surface to the discharge is real head, and it is not included here.
When one pump cannot reach the top
The 350 psi working pressure ceiling is what forces zoning, and it arrives sooner than the height of the building suggests, because the churn multiplier eats the margin. Work backwards: allow the 100 psi residual, allow friction, allow the 140 per cent shut-off, and a single zone runs out somewhere around a hundred metres of lift. Beyond that the main is split, and the split is a real building decision rather than a valve.
Two arrangements dominate. An express riser carries water from the ground plant to an intermediate transfer tank part way up the building, where a second pump set serves the upper zone from a fresh datum; or a series arrangement pumps into the base of the upper zone directly. Either way the upper plant room is a rated enclosure on an occupied floor, with a tank on it, standby power to it, and access for a crew — which is floor area the letting agent had other plans for. Each zone then carries its own pressure-regulated landing valves in its lower third, its own inlet for the brigade to boost, and its own commissioning record. Two zones is not twice one zone; it is two systems that happen to share a shaft.
Hanging five tonnes of steel and water in a shaft
A dry main is deceptively light. A 110 m run of 150 mm schedule 40 steel is about 3.1 tonnes of pipe, and the clamps hold that from the day it goes in. Charge it and it gains 2.1 tonnes of water, and a wet main carries that load permanently. The supports are not a detail to be resolved on site by whoever has the longest drop rods.
Vertical support comes off the code table, not off habit: NFPA 13 sets where risers are clamped relative to floor levels and offsets for sprinkler and standpipe work, and the IPC hanger spacing table governs the horizontal run at the base by material and size. What the calculator below does is turn a spacing interval into a count, which is the number you order against — and on a riser clamped at each floor level it is simply the storey count plus the offsets, which is worth checking against the frame rather than assuming a regular floor-to-floor. Add supports at every change of direction, at the pump connection and either side of the base valve; the table gives the straight-run minimum and nothing else.
Two things happen at each floor that are not support. The main passes through a compartment floor, so the penetration is a tested and certified seal — to BS EN 1366-3 in the UK, to ASTM E814 or UL 1479 in North America — and steel pipe takes a different seal from plastic, since there is no wrap or collar behind it doing anything. The firestop guide covers how those systems are chosen and what invalidates them. And the pipe moves: a main charged with cold water in a shaft that runs warm changes length, so the difference between a guide that lets it slide and an anchor that does not has to be drawn rather than left to the fixer. Where seismic restraint applies, that is a third set of components again, sized under ASCE/SEI 7 and the bracing provisions of NFPA 13.
Take the maximum spacing from the applicable code table for the pipe size and material, put in the run, and the answer is the clamp count for the order. It is a straight-run figure by design, so add the supports at offsets, at the base valve and either side of the pump connection separately.
The total length of the pipe run needing support.
The maximum spacing between hangers allowed by code for this pipe's material and size.
Pipe hangers needed
10 hangers
Maximum hanger spacing depends on your pipe's material and size per the applicable plumbing/mechanical code table (e.g. IPC Table 308.5) — confirm the correct maximum spacing for your specific pipe before finalizing hanger count.
- Bays along the pipe run
- 9
- Hanger centres along the pipe
- 7.33 ft
They open the calculator with your figures already in it
Pipe Hanger Spacing Calculator: 10 hangers — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- The +1 in the count assumes a hanger sits at each end of the length you typed, so a line measured and entered in sections will be over-counted by one hanger at every join where two sections meet and share a single support.
- One spacing figure is divided into the whole run, which means a line that steps down in bore partway, changes material at a transition, or turns from a horizontal leg into a riser has to be entered as separate runs and the counts added — the arithmetic cannot hold two permitted spacings at once.
- Weight never enters the calculation: no bore, wall thickness, contained water or insulation is asked for, so the answer gives the number of support points and says nothing about rod diameter, hanger type, or whether the structure overhead can carry a filled line.
- The centres reported are an even division, which is why they come out under the maximum rather than on it: a 20 m run at a 2.4 m maximum is nine bays at roughly 2.22 m. Marking from one end at the full maximum instead is the other way to do it, and it leaves a short final bay to absorb — the page does not price that choice, and on a line with a fixed anchor at one end it may not be yours to make.
- The spacing box refuses anything above 4 m (about 13 ft) and the run length stops at 200 m (about 656 ft), so a longer continuous line, or a support interval wider than that ceiling, has to be broken into pieces and counted piece by piece.
The tests that decide whether it was actually built
A rising main is one of the few installations that is genuinely never used by the people who own it, which means the only evidence it works is a test. NFPA 14 acceptance is a hydrostatic test at 200 psi held for two hours, or 50 psi above the maximum system pressure where that exceeds 150 psi, and for a dry system an additional air test at 25 psi held for 24 hours with no more than 1½ psi lost. Automatic systems then get a flow test that demonstrates the residual pressure at the hydraulically most remote outlet at system demand — the acceptance test, not a calculation of it. BS 9990 sets the equivalent regime for UK installations, with a six-monthly visual inspection and a full pressure test of the installed main annually.
In service, NFPA 25 asks for a five-year hydrostatic test on manual and semiautomatic dry standpipes at 200 psi for two hours, and a five-year flow test at the hydraulically most remote connection of each zone of an automatic system. Fire pumps run to their own cycle of no-flow tests and an annual flow test at churn, rated capacity and 150 per cent of rated capacity — the three points NFPA 20 defined the curve at, checked against the curve the pump was accepted on.
- Confirm the inlet position against the actual hard standing and the actual finished landscaping, not the layout that was priced.
- Pressure test the main before the shaft walls close, and photograph every joint and every clamp while they are still visible.
- Firestop each floor penetration to a tested system, record the system reference, and photograph it before the ceiling goes on.
- Fit and cap the air release valve at the head of the main, and prove there is a drain at the base that falls to somewhere water can go.
- Hydrostatic test the completed installation at the standard's pressure and duration, then air test a dry system and hold it overnight.
- Flow test an automatic system at the hydraulically most remote outlet and record the residual pressure at the system demand, not at churn.
- Set, label and record every pressure-regulating landing valve by floor, in the manual and on the record drawing.
- Run the fire pump at churn, at rated flow and at 150 per cent through the test header, and file the curve against the accepted one.
- Hand over the operation and maintenance manual with the test regime, the valve settings and the inspection intervals written where a caretaker will find them.
What to have settled before the shaft walls close
Height, position and duty, in that order. The first is a survey figure, the second is a site layout agreement, and the third is a room in the basement that has to exist on the general arrangement before the piling rig arrives.
- Vertical distance, inlet to the highest landing valve — Measured to the outlet, not to the roof or to the top of the shaft. This is the number that chooses dry against wet and it is a survey item, not a drawing item.
- Fire service vehicle access level and the hard standing position — The datum every height threshold is measured from, plus the standing an appliance will actually occupy. Both belong on the site layout, agreed with the fire service.
- Design flow, and how many outlets run at once — The demand that sizes the bore, the pump and the stored volume. One remote outlet is not the design case in any code.
- Bore, material and Hazen-Williams coefficient — Real internal diameter rather than nominal size, and the lower coefficient if the main is black steel standing dry between uses.
- Floor-to-floor heights and the offset positions — The clamp count comes off the frame, and a transfer level or a stepped shaft changes it in a way a regular spacing will not catch.
- Total head at the top outlet, split into lift, friction and residual — Three components written separately, because the pump schedule, the pressure-regulating valve schedule and the zoning decision each read a different one.
- Plant room footprint, tank volume and power arrangement — Flow times duration gives the tank, the tank gives the room, and the room has to be on the basement general arrangement before the layout is fixed.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.