Fire Pumps Minium Flow

[Smokerr]

This is an issue that confounds me and others I have talked with but has very little exposure and as far as I can tell no recognition in the codes.

I came across this the in the forum "thread407-292211"

In our case we have found extensive damage to the intake of the pumps around the wear ring as well as severe erosion of the vanes in the pumps (flow diverts, cut-waters, it seems there are a number of names for the 90 degree devices sticking out into the flow).

In the thread the comment was that it was stupid to run the pump when you did not have to.

You are obligated (though often not done) to run these 30 minutes a week (diesels).

In our case, we are also obligated to maintain protection and if we dump water (and winter is impossible) we are creating an impairment to the building we are supposed to be protection.

If it was mandated that at minimum there be a recirculation loops (with a flow meter so you can determine what your flow is) that would prevent it. Better yet would be a line back to the tank.

With the damage to the pumps and no viable solution you have to repair if possible and then replace expensive pumps. That should not take place. My take is no pump MFG wants to say his pump needs to recirculate and others not say anything and put themselves at a competitive disadvantage (read that no pump sales)

I talked to an engineer who formally had a job where he tested and repaired systems. His comment was that most of the systems he worked on had issues.

Its hard to see as the deterioration is slow and the system still meets the NFPA specs, but if actually compared to the original test cures you can see the degradation and in fact its tearing itself apart inside.

I think this subject should have a lot more discussion and exposure. I see the committees meeting a coming up with all sorts of nit noid updates when there are serious issues that are not addressed.

 

[BigInch]

"Better yet would be a line back to the tank." Or possibly to suction, but that would probably limit run time at one go to 10 min, or less, so that's 3 times a week.

That's what is required. Do it, live with it, or don't run at all.

Independent events are seldomly independent.

 

[Smokerr]

I certainly appreciate the input.

As its a violation of NFPA and the AHJ (not to mention company policy that mandates the system actually be checked and tested to ensure it will function in the event of a fire that takes the don't run at all off the table.

Its obvious we have to live with it and we have put in for the fix (so I figured that one out).

Any donation to help out with the getting it fixed would be greatly appreciated.

The point is that its an issue that should not occur as it should be mandated by NFPA. They mandate every nut, bolt, washer etc be UL/FM approved and then let something gross like this go past.

We have multiple pump system so we have some options as far as having one down for repair or replacement.

A single pump system does not have that and you have to wonder about all the obsession with the other aspects when the pump falling apart will stop the protection every bit as disastrously as a motor/engine not starting, air entrapped, loos of power, loss of water etc.

 

[LittleInch]

Smokerr,

I can see your issue and every time I dip my toe into the world of NFPA pump systems and fire water design, I see your point which I think is a result of the fire protection code separating itself from other forms of piping design and pump design.

Having said that it is also the responsibility of any engineer to design something that can be operated without causing any injury and within the operating parameters of the equipment. This is imply good practice. The latter side seems to have got lost a bit with respect to the requirement to run a pump for a specified period, without any real flow through the system.

Any pump after a relatively short perod (1-2 minutes at most) needs to have re-circualtion otherwise damage will occur to the pump, it's bearings or associated equipment. Any positive displacement pumps need this as a matter of design otherwise severe over pressure of the downstream equipment could occur.

Re-circualtion for the time you specifiy should require at least 30% of rated flow going through the pump and inclusion of a cooler if required to prevent temperature build up. The point to make to people is that the engine is running and providing energy into the system, but where is tat energy going - answer - heat of the water. This is like running your car at full revs whist chained to the wall. Either your tyres will burn out and explode or the clutch / gearbox will blow up if you do that too often and then it won't go at all....

The point where this needs to come up at the very least is in the HAZOP of the fire water system. It is not an acceptable response to simply say "its as per NFPA XX" and not address the specific HAZOP action arising from No flow, high temperature, Other (damage to pump).

You might need a strong HAZOP chairman to note this and follow through on actions, but is the only way I can see it going without significant NFPA code action change.

Good luck and keep the faith...

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[EdStainless]

surely in the manuals for the pumps there is a minimum rated flow. Most pump curves have a cut off distinctly marked on them. They pump guys are assuming that the system has been designed to respect these values.
Dumping the recerc line back to the tank helps minimize heat build up but involves more piping.
Perhaps one return to tank line that is connected to all of the pumps? But you still need individual relief valves.
Then you also have to show that in use your recerc vales would close and reduce usable flow.


= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[Smokerr]

LittleInch and EdStainless:

Thank you both for the thoughtful responses.

LittleInch: I am not familiar with the HAZOP term (I am more a technician than my "title" of engineer which comes sans any letters to go with it.). Hazards to Operation?

Ironically our system uses a heat exchanger with supply from the discharge of the fire pump. That keeps us well away from any heat buildup in the pump (though it then adds the issue of etching out the coolant piping as its 180 psi requiring that cooling line piping be replaced every 5 years (I would add that is another aspect that while it works has a set of hazard issues all its own and I think its a really bad idea to allow that instead of a radiator system (my take is that its cheaper at a catastrophic price if any one of a number of failures occurs and guaranteed a destroyed pump if your water supply gets depleted).

We have been working towards that goal of getting a recirc loop in (economically not feasible to do a run back to the tank, partly due to the climate). If we can get the recirc loop we think we would be in pretty good shape.

It seems NFPA does not have good engineers and technical people on the board (or so few they are not heard).

At least locally the fire dept was dead against Recirc loops (for a testing proof but I have to wonder if that plays in on the bias against them generally) They contended it did not in fact really make the pump work/ flow (amp draws and RPM drop on a previous electric driven pump proved that wrong). I have to wonder if it’s a degree of ignorance of how thing work and FD types bias against the reicrc loop playing into this.
I did contend that in turn their flow test with a filed test header was no better as it was all based on calculations and the only real verification would be to dump it into a tank and time it.
They did have to admit that the recirc flow rates and associated amp draw matched their flows/amps readings very closely.

EdStailnless:

We have replaced one pump and the latest submittal that came with the new pump does list to a minimum flow rate (that was not with the original books and or data submitted) so that data is now being supplied.
. My suspicion is though unless its actually mandated code to flow at the minimum for testes, all that does is ensure the FP supplier can then say, the damage is a result of no flow and the pump mfg is off the hook (and rightly so if they do indeed supply that information and nothing is done with it).
Unless it becomes mandatory that you have to design a system that deals with that minimum flow they will still get designed as dead headed for testing.

 

[LittleInch]

HAZOP means hazard and operability study, which can be done any time, but usually as part of design or modifications to carefully examine all aspects of a design for e.g. no flow, low flow, excess flow looking for things that cause it and things included in the design to prevent it or mitigate it, e.g. preassure switches, alarms, shutdowns etc. Look it up and it may help you in your drive to make things better.

Recirc loops have a bad reputation if not designed and maintained properly, but you can't expect FD people to be pump experts so probably just don't understand the basics.

Codes are really only the minimum standard and should not replace good engineering practice and design, but are sometimes used to justify lack of thinking and appreciation of design issues.

All you can do sometimes is insist that the design being supplied would lead to failure of parts unless mandated operations such as regular testing can be done without damage to the pump...

Good luck

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way