Thread: sprinkler system pressure

I sometimes see pressure guages on sprinkler systems that read 100psi or more. I then test the pressure at a hose bib and find it to be lower at 60-80psi.

Are the sprinkler systems pre pressurized at the higher level and held that way with a check valve or something?

The sprinkler system gets its supply from the same source and I wonder how the pressure can be different at the hose bibs.

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Originally Posted by John Dirks Jr

I sometimes see pressure guages on sprinkler systems that read 100psi or more. I then test the pressure at a hose bib and find it to be lower at 60-80psi.

Are the sprinkler systems pre pressurized at the higher level and held that way with a check valve or something?

The sprinkler system gets its supply from the same source and I wonder how the pressure can be different at the hose bibs.

#1 Sprinklers are required to have a backflow preventer installed, so the pressure could read higher due to thermal expansion or the pressure was higher earlier.
#2 The house could be on one meter with a PRV and the sprinklers could be on a separate meter without a PVR.
#3 Pressure guages (yours and at the sprinkler) are not very accurate.

Originally Posted by John Dirks Jr

I sometimes see pressure guages on sprinkler systems that read 100psi or more. I then test the pressure at a hose bib and find it to be lower at 60-80psi.

Are the sprinkler systems pre pressurized at the higher level and held that way with a check valve or something?

The sprinkler system gets its supply from the same source and I wonder how the pressure can be different at the hose bibs.

Sounds like you have a standalone system which excludes the combined residential plumbing and sprinkler you see on one and two family dwellings.

Assuming a standard sprinkler system this is not unusual. I've seen pressures well in excess of 200 psi. You should know this is more common than one might think.

NFPA standards require 175 psi PRV's be installed on wet pipe systems that are gridded designs.

Originally Posted by Arthur Gould

I've seen pressures well in excess of 200 psi.

150 psi to 175 psi is common for fire sprinkler systems, and they are tested at 200 psi to 250 psi.

Originally Posted by Jerry Peck

150 psi to 175 psi is common for fire sprinkler systems, and they are tested at 200 psi to 250 psi.

Depends on the system.

If it is installed per NFPA #13D (one and two family dwellings)

4.3* Hydrostatic Tests.
4.3.1 Where a fire department pumper connection is not provided, the system shall be hydrostatically tested for leakage at normal system operating pressure.
4.3.2 Where a fire department pumper connection is provided, the system shall pass a hydrostatic pressure test performed in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems.

Normal system pressure would be city water pressure which normally runs between 50 and 100 psi.

As far as a one or two family dwelling is concerned I have never seen one equipped with a fire department connection in over 35 years.

For standard systems installed per NFPA #13

10.10.2.2 Hydrostatic Test.
10.10.2.2.1* All piping and attached appurtenances subjected to system working pressure shall be hydrostatically tested at 200 psi (13.8 bar) or 50 psi (3.5 bar) in excess of the system working pressure, whichever is greater, and shall maintain that pressure without loss for 2 hours.

With very few exceptions systems are designed for a maximum working pressure of 175 psi and it is seldom pressures exceed 150 psi. I would estimate a 200 psi test will cover 98% of systems installed.

By and large most sprinklers are rated for a maximum working pressure of 175 psi and while it is possible to obtain heads listed to 250 psi they cost a lot more money but that is the least part of the problem. Again, in 35 years I've never designed a system for a working pressure greater than 175 psi.

Originally Posted by Arthur Gould

As far as a one or two family dwelling is concerned I have never seen one equipped with a fire department connection in over 35 years.

I've only tested sprinkler systems installed in one and two family dwellings a few times, and that was well over 10 years ago, and there were only 5 of houses in the development.

I would estimate a 200 psi test will cover 98% of systems installed.

All the other sprinkler systems I've tested (not that *I* as the inspector "test" them, but I check the pressure and look for pressure drop and leaks) have been for condo, from 2 story condo buildings which would otherwise be thought to be townhouses if you didn't know they were condos, to highrise buildings with standpipe systems. All were over 200 psi (I suspect the installers did not want to fail the test by not-quite-being-at-the-200 psi pressure, so they increased the pressure higher. Several took the pressure to 250 psi as I recall. I checked the pressure at the beginning of the inspection (typically, the systems were pressurized the day before), checked the pressure part way through the inspection, and then again at the end of the inspection (I was also doing other inspections, so I was on-site for more than the 2 hours, and in addition to the other inspections I would check for leaks - sometimes there would be a leak part way through and they would need to release the pressure, drain the system, replace the leaking component(s), then start over at another inspection.

I saw one once where they had just repaired the system earlier in the day and were pumping it up for a re-inspection the next day, and ... POW! ... another fitting blew off because it had not been glued on properly. I have no idea what pressure it blew off it, but it certainly did get the attention of everyone on the job!

Originally Posted by Jerry Peck

All the other sprinkler systems I've tested (not that *I* as the inspector "test" them, but I check the pressure and look for pressure drop and leaks) have been for condo, from 2 story condo buildings which would otherwise be thought to be townhouses if you didn't know they were condos, to highrise buildings with standpipe systems. All were over 200 psi (I suspect the installers did not want to fail the test by not-quite-being-at-the-200 psi pressure, so they increased the pressure higher. Several took the pressure to 250 psi as I recall. I checked the pressure at the beginning of the inspection (typically, the systems were pressurized the day before), checked the pressure part way through the inspection, and then again at the end of the inspection (I was also doing other inspections, so I was on-site for more than the 2 hours, and in addition to the other inspections I would check for leaks - sometimes there would be a leak part way through and they would need to release the pressure, drain the system, replace the leaking component(s), then start over at another inspection.

It isn't unusual to see pressure rise during a test. Fill the system in the morning and as the temperatures rise so will pressure. Setting it at 205 psi only to find it at 220 psi a couple hours later is rather common.

saw one once where they had just repaired the system earlier in the day and were pumping it up for a re-inspection the next day, and ... POW! ... another fitting blew off because it had not been glued on properly. I have no idea what pressure it blew off it, but it certainly did get the attention of everyone on the job!

It is easier to miss gluing a joint than one might think and the bad thing about cpvc is I've seen unglued fittings hold for weeks and even months before they finally give way.

Some might know this but why are systems tested to 200 psi?

Leaks aren't the big issue, leaks will be repaired because the owner won't stand for it, but the real reason for a 200 psi test is to insure the integrity of the system when the fire department hooks their 2 1/2" fire hoses from the pump truck to the fire department connection.

You've all seen them they come in Wall Mounted



or yard stand alone



The most common have two (2) 2 1/2" inlet connections but it is not uncommon to find a single 2 1/2" inlet, or even a single 1 1/2" inlet, on some systems that produce smaller demands.

They sort of look like hydrants but what fire departments do is run a 5" line from the pumper outlet on a hydrant to their fire truck. From the fire truck the fire department will run two 2 1/2" hoses to the fire department connection so they can boost pressure.

The most common boost is 150 psi.

A single 1/2" sprinkler will discharge 39 gpm at common city pressure of 50 psi but if the pressure is boosted to 150 psi that same sprinkler will discharge 68 gpm.... more water means more effective fire fighting.

The reason for the hydrostatic test is to insure a fitting won't blow off in a fire fighting operation... the last place you want to see a system impaired.

From a inspection standpoint fire department connections are required to have caps or plugs to prevent debris from being introduced to the piping system. Also the swivels should operate freely (they spin allowing the hose to be attached) which I know most inspectors avoid fire sprinkler/standpipe systems but this would be something worth mentioning in passing.

A lot of these are being stolen. Most are solid brass and they've taken to disappearing for scrap.