Jockey Pump on a Dry Pipe System 1

[sl3656]

Does a dry pipe system need a jockey pump? I am certain not, since there is no wet sprinkler pipe that needs pressure maintenance for small leaks etc. However, would appreciate any thoughts on this. Thanks.

 

[LCREP]

Dry pipe system require an adequate water supply which MAY include a fire and jockey pump. Dry pipe system also need an air supply which can be an air compressor, bottled nitrogen, etc. to keep the dry pipe valve shut.

 

[jzlomie]

If it helps at all, I have also heard numerous individuals refer to the air compressor as the "jockey pump" on a dry system. Other than that or if the system has a pump on the supply side, I can't think of a reason why there would be one.

 

[DavidCR]

Good question. Don´t have the answer. The main pump start point refers to JP set point to define start. If there is no JP how do you define start for the main? How do you keep the pipe upstream of the control (preaction) valve full?

 

[stookeyfpe]

A dry pipe valve doesn't need a pressure maintenance pump as defined in NFPA 20. A pressure maintenance pump is not required by NFPA 13 for a dry pipe valve. A reliable source of clean, dry air or nitrogen is required for a dry pipe valve per NFPA 13 Chapter 7.

 

[DavidCR]

So the line between the pump and the upstream side of the preaction valve is also dry? If so when the pump starts the water would fill or refill violently the pipes, is that Ok? I am missing something?

 

[stookeyfpe]

I'm not sure why a fire pump is being mentioned. A pressure maintenance pump (a.k.a., jockey pump) is only required for a NFPA 20 fire pump installation. It has no relevance to a dry pipe valve. The original poster asked a question and used components that don't have a relation to each other.

All dry pipe valves (DPVs) require either an air or nitrogen source to maintain the minimum required differential pipe so the valve's seat is maintained in the closed position. This pressure is based on the static pressure of the water supply. Below the valve seat, the pipe is filled with water; above the DP valve seat or diaphragm, the pipe is dry. Activation of a sprinkler begins to exhaust the air or nitrogen, which reduces the pressure below the required differential pressure and as a result, the DPV is opened, water fills the sprinkler pipe and discharges through the open orifice.

 

[cdafd]

https://m.youtube.com/watch?v=KwYFvW5einQ

 

[DavidCR]

I understand that downstream the dry valve the jockey pump is not involved nor needed, my doubt is if if the water supply (upstream) this valve need a pressure maintenance pump.

 

[UFT12]

Forget about the dry valve. Forget about valves of any kind. Who is going to replenish the pressure loss of your underground service main which could leak like hell?

 

[MGXFP]

I think what you may be referring to is a pressure pump used for dry pipe systems converted to wet pipe systems. I've seen literature from the '70s and '80s allude to this. It is a small pressure pump to boost pressure downstream of a dry valve clapper to avoid accidental alarm trips when underground pressures surge.

If this is the case I suggest removing the dry valve entirely and ensure adequate heat is maintained.

 

[sl3656]

Not sure how this thread got "resurrected" per se.

Just to clarify, I already know that a air or nitrogen compressor is required for pressure maintenance, downstream of the dry-pipe valve.

I was asking whether a jockey pump is required - as is typical in wet pipe systems. Having a jockey pump on a dry system, to my understanding, would only serve to maintain pressure between the dry pipe valve and the pump - i.e. inside the pump / valve room only. I am not sure whether there would be in any value in this. In any case, I have already included one in our design, essentially to have pressure maintenance on the wet part of the dry pipe system.

 

[LCREP]

A jockey pump is NOT required and serves no purpose as you have described your system , as a plan reviewer if I saw this I would start to look very closely at the rest of your plan .......

 

[sl3656]

@LCREP - thanks for your candid feedback.

May I ask, is there any code citation that says it is NOT required as you say? The jockey pump would still regulate against leaks within the wet side of the system, albeit within the pump room itself, as well as providing possible future proofing in case the building would require a wet system from the header manifold.

 

[LCREP]

The only time a jockey pump is required by NFPA 20 is when you have an automatic starting fire pump. A drop in water pressure starts the jockey pump and if the water pressure can not be maintained the fire pump starts. If you have a public water supply without a fire pump which is adequate to meet the required GPM and psi to meet system demands weather a dry, wet, preaction a jockey pump is not required on the water supply side of the fire protection valves.

 

[sl3656]

@LCREP - I do have an automatic fire pump feeding the dry pipe valves on the wet side of the system, as the pressure from the city main via the private fire main connection is insufficient.

 

[DavidCR]

That is what I was seeing, depending on how big is the system between the pump and the dry valve, you have a wet system to consider or not. Where is the limit? Other point is if the DPressure of pump at the start is too big, is it recommended to have JP to define a good star set point for the main valve?

 

[LCREP]

David CR

See NFPA 20 2013 ED section A.14.2.6 for how the jockey and fire pump pressures should be set, see below. Once this is done the dry pipe valves should be set for the max churn pressure of the fire pump. This is critical when dealing with dry systems, my experience is the jockey pump pressure is set too low when the fire pump starts the water hammer can be significant to trip the dry pipe tvalve. Hope this helps.

Examples of fire pump settings follow (for SI units, 1 psi = 0.0689 bar):
i. Pump: 1000 gpm, 100 psi pump with churn pressure of 115 psi
ii. Suction supply: 50 psi from city — minimum static; 60 psi from city — maximum static
iii. Jockey pump stop = 115 psi + 50 psi = 165 psi
iv. Jockey pump start = 165 psi − 10 psi = 155 psi
v. Firepumpstop=115psi+50psi=165psi
vi. Firepumpstart=155psi−5psi=150psi
vii. Fire pump maximum churn = 115 psi + 60 psi = 175 psi
Where minimum-run timers are provided, the pumps will continue to operate at churn pressure beyond the stop setting. The final pressures should not exceed the pressure rating of the system components.

 

[SprinklerDesigner2]

I think I might have finally figured out what the OP wanted to know.

It has nothing to do with fire pumps or jockey pumps.

Years and years ago I remember a project we did that was at the end of a dead end line that suffered surges that would set off the waterflow switches. What we ended up doing was installing a small water pump to boost the pressure on the system side to 140 lbs so when a water hammer happened boosting the pressure from 50 psi to 110 psi no water would flow so we didn't get an alarm.

Was it the right thing to do? It was back in the 1970's and that is all I remember.

The OP wants to know if something like this is needed on a dry system and the answer to that is no.

 

[LCREP]

SprinklerDesigner2

Just about every building in Massachusetts i.e. think Boston with a "Gamwell" municipal pull box fire alarm system connected to the wet sprinkler riser has what you describe to prevent false alarms. Very strange the first time I saw it many many years ago. These systems are like 100 years old and still in service well at least 3-4 years ago when I was in Boston doing inspections.