Fire pump and a domestic system 1

[m2e]

Hi,

I'm designing pump station where it has 2 duty pumps for domestic water use of a community. The system contains hydropneumatic tanks. There is also a fire pump in the pump station tied in with the same suction and discharge pipe. Do I still need jockey pump or would the domestic pumps with the tanks able to maintain system pressure?

Thanks.

 

[pipesnpumps]

No jockey pumps are needed for "fire pumps" installed in potable systems. The domestic pumps maintain the pressure.

Don't have books handy or I would cite NFPA 20 section, but I have dealt with this before.

There really is no hard requirement to use a true fire pump though.. NFPA requirements don't apply to domestic water supplies.

It must be a small community, since I am assuming that the firewater demand is greater than the peak domestic water demand.. So the only time the "firepump" would run is for a large fire. In that case it would be beneficial for it to be an NFPA 20 pump, that is tested and maintained to be a stand-by firepump.

However, if the domestic water demand is higher than the firewater demand, then the "firepump" would turn on whenever say, people are watering their grass. It would be better for this to be a normal potable water pump.

The only time I have seen a setup like you are talking about (potable pump + fire pump feeding the same underground) is a large industrial complex with a small potable water demand, but large firewater demand..

I would urge you to look closely at the numbers to see if it would be best to simply put in a potable water pump.

 

[m2e]

The pump station is in fact serving a small community. The fire pump flow is 30 time of the domestic water demand.

Now, checking with utilities, only single phase power is available at the site. The pump is 50hp.

Q1. Is phase converter (VFD) allowed in NFPA fire pump station?

Also, I'm very confused about pump testing equipment. Some people say flowmeter can replace hose connection, but I also read that you need an annual test of the source water. There was also an option to pipe the water back to the reservoir. We have a reservoir next to the station.

Q2. In what situation would you put in a flowmeter instead of a hose connection?

Q3. When do you need hose connection?

Q4. Is piping the water back to the reservoir an option? If so, do I still need the hose connection?

Thanks.

 

[pipesnpumps]

Q1: can't answer the phase converter, although search here, there was a discussion earlier this year on that.

Re: flow test. You can flow test the pump in a closed loop (back to the suction), but once every 3 years you have to actually flow the water through hoses or back to the reservoir/tank to prove the water supply line is open and operational. I have personally never heard of testing the "source" water, if you mean the potable water line feeding a firewater storage tank..

However, since your reservoir is not a firewater tank, then you should design to test the firepump via a test header with hose valves on the downstream side of the pump.. In other words, treat it just like a firewater booster pump.. Everything upstream of your "fire"pump is simply part of the potable water supply (within the scope of AWWA). Functionally it is no different than an underground supply line. So the hose valves are a must, and a closed-loop meter is optional. This would allow the pump to be tested every year, and only drag out the hoses and flow water every 3rd year.

If you had a firewater tank and firepump installed in a set, then you could recirc back to the top of the firewater tank with an inline flowmeter and never have to hook up hoses, but you don't have that situation. In addition to the test header and hose valves downstream of the pump, some people like to install a recirc from the pump discharge back to the suction.

As I mentioned in the previous post, this pump is really part of the potable water supply and not part of a private service fire main. You are in a grey area, because technically the argument could be made that this potable water pump is not required to meet NFPA 20&25 standards, but if it were to simply meet AWWA standards it would not be as likely to be tested..


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Additional info:

Every fire pump installation needs a method for performing the acceptance test required in Chapter 14. NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, permits the following three methods for testing fire pumps.

1. Test header.
This device is connected to the discharge side of the pump and has a number of hose outlets. When testing the pump, the hose is connected to the outlets with water discharged in a safe location. Flow readings are usually taken from the end of the hose with a Pitot tube or other flow measuring device.

2. Flowmeter.
A special pipe is run from the discharge side of the pump back to the water supply (or to some other acceptable discharge point) with a flowmeter, control valve, and check valve in the line. When testing the pump, the control valve is opened partially (with the pump already running) to achieve the 100 percent flow condition. The valve is then opened more to achieve the 150 percent flow condition.

3. Closed loop metering.
This method consists of a bypass line with a flowmeter, control valves, and a check valve that goes directly from the pump discharge to the pump suction. This test is run the same way as method 2, but the water does not come from the supply. The water is recirculated in a small loop through the pump.

It should be noted that A.5.19.1.2 recommends that metering devices discharge to drain, to the water supply tank, or to the outside.

Because closed loop metering (method 3) does not test the water supply’s ability to get water to the pump, NFPA 25 limits its application. Once every three years, testing must be done in accordance with method 1 or 2. This requirement means that the designer must make sure that equipment to perform the annual flow test in accordance with method 1 or 2 is included in the original design or, three years after installation, the building owner will not
be able to comply with NFPA 25.