Maximum Allowable Pressure for Fire Hydrant?

8/1/2022

We have a proposed fire hydrant in our county that will have pressures ranging from 210 psi to 250 psi according to the engineer designing the underground line.

My Chief and I are looking into this in regards to NFPA standards/applicable code, and are concerned that the high pressure could injure firefighters or damage equipment.

Is there a maximum permitted pressure that a hydrant can be, per code?

Thanks in advance.

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9 Comments

Alex

8/1/2022 06:54:37 am

Hi,

Is the hydrant downstream of a fire pump or part of a combined standpipe system?

NFPA 24 (2019) A.10.1.2 states "systems that do not incorporate a fire pump or are not part of a combined standpipe system do not typically experience pressures exceeding 150 PSI in underground piping."

Materials used for an underground system are rated for no less than 150 PSI. If you are exceeding 150, ensure that all pipe materials are cleared called out to handle the additional pressure. There is no maximum pressure listed in NFPA 24.

I would ensure you are within your operating range of all components, of all apparatus, within your department. For example, my call department has an engine with an intake valve with a maximum of 250 PSI.

Thanks,
Alex

chad

8/1/2022 08:12:57 am

I concur with Alex.

We have the same issue with a large industrial facility that has all its yard hydrants and sprinkler riser fed from the pump off the same main fed from municipal water (its old). we get 190-200 PSI out of hydrants and cant adjust relief valves high enough to keep them from operating. But the trucks can safely handle it.

Unfortunately they need that head pressure to overcome FL for the sprinkler due to distance and elevation. No one has the willingness to make them split the yard hydrants off on a separate line with a PRD.

Is it only 1 hydrant like this? You didn't say hydrants.

Glenn Berger

8/1/2022 08:11:01 am

Delivered pressure of 210 to 250 psi is way to high. Need to ensure that the hydrants provided can support that pressure and that the Fire Department approves.

Sounds like the project is installing a long distance water transmission pipeline. Fire Hydrants should never be installed on these pipes.

Greg

8/1/2022 08:35:14 am

I'm in agreement with Glenn that the pressure is too high. My experience with similar pressures as noted by Glenn was in a transmission type pipe in Nevada. The water's source was elevated in a nearby mountain range and the main transmission piping network had very very high pressures. The water sent to the fire hydrant networks required pressure reduction.

The top pressure number in the question, 250psi, I believe is the rated pressure limit for many standard hydrants. Reducing to 200 or below with a goal of 175psi is something that is manageable.

How to accomplish the reduction feels more like municipal water equipment than traditional fire water supply equipment but likely there is someone here who can call out a make and model that speaks to the question.

Aaron

8/1/2022 09:14:01 am

As an engineer who has decades of municipal and private experience with transmission, distribution and point of use I can say that something sounds quite off here.

My first question is why is a hydrant being proposed at this location to start with...is there a structure at risk or is it to adhere to a blanket spacing requirement along a new public line?

The second question is in line with what others have mentioned...this sounds like a transmission main which in principal is not tapped except for installation of a master meter (which will include pressure reducing valves) to a secondary pressure zone. This secondary zone would then have distribution piping onto which hydrants would be installed.

IF for some special reason this singular hydrant is indeed intended to be installed on this high-pressure main, all fittings and pipe must be minimum Class 250 rated, and I would recommend the installation of a FM-rated double detector check valve assembly followed up by a pressure reducing valve assembly with a FDC and/or ground hydrant for connection.

All of this new infrastructure will require protection from freezing as well as being located in a secure location to avoid vehicular impact (including brush hogs if in the ROW).

If you have additional details on the application we can provide a more tailored approach.

Fred walker

8/1/2022 10:13:59 am

There are some cities like Baltimore and San Francisco (there are others) which operate high pressure / high volume fire protection water distribution systems separate from the potable distribution systems. Some of these are capable of pressures you have indicated.

As well there are industrial fire protection water distribution systems capable of similar pressures.

One option would be to require intake relief valves designed for a greater pressure range than standard off the shelf relief valves.

Jesse

8/1/2022 01:45:35 pm

I concur with Alex. This is too high

Dwight

8/1/2022 07:02:59 pm

Ever been on the business end of a manual hose line with 175 psi on it? It is not fun, and totally unproductive. In fact, it is on the borderline of dangerous. For fixed appliances it can work, but not for a mixture of the two (manual and fixed). For manual firefighting the nozzle pressures typically vary between 50 psi for straight bore and 100 psi for fog tips. Even at a supply pressure of150 psi, your discharge pressure from the engine will be about 175 psi, at idle.

I had one case where the design engineer oversize the pressure output of a stationary fire pump feeding a large standpipe system. He refused to downsize the pump and instead installed a pressure regulating valve, adding significant complication to the system that didn't need to be there, and the need for additional inspection, testing and maintenance maintenance for the life of the system.

Jay

8/2/2022 10:45:41 am

Our fire engines have intake relief valves set at 145psi, so that's something you'll want to look into cause you'll be dumping water like crazy. Also think about the LDH you'll be using to connect the hydrant to the pumper.....what is its maximum working pressure?

Maximum Allowable Pressure for Fire Hydrant?

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