How to start vertical fire water pump and remove air? 2

[bizkitgto]

We are installing a new firewater system as part of a plant expansion. The new firewater system will draw fire water into a sump fed from storm ponds, this sump will feed both main fire pumps and jockey pumps. The pumps are all vertical centrifugal pumps. Since these pumps will always be submerged and primed, and the discharge piping will be water full, how does one remove the trapped air that will always exist between the sump water level (below grade) and the discharge piping (above grade)? How does an auto-start guarantee removal of air when feeding into the main fire main piping?

Each pump has a dedicated spill-back line for start up, but talking with operations there is disagreement on how to best start the pumps. Normally we start pumps with discharge blocked in, and slowly open the discharge valve on spill back, but here, there will be a large section of piping full of air, and I am concerned this will cause a major surge.

Any ideas on how best to start vertical pumps with a major section of air in the system? I am surprised NFPA doesn't address this, as most fire water systems pull from ponds and have a similar setup. Any advice?

 

[bimr]

Air/vacuum valves are installed on the discharge of vertical pumps before the check valve to vent the air from the pump column during the starting of the pump and to admit air into the column to dissipate the vacuum upon stopping the pump.

Air/Vacuum

Link

 

[MortenA]

Be aware of possible pressure surge when you water "hits" the air/vacuum valve it will close and/or the nozzle this will result in a sudden deceleration of the water column and this could cause a pressure surge. This is mostly relevant if the elevation difference is significant say more than 10 m.

--- Best regards, Morten Andersen

 

[pierreick]

HI,
Consider this link

https://www.valmatic.com/Portals/0/pdfs/AirValvesforVerticalPumpApplications_18.pdf

Pierre

 

[LittleInch]

biz,

I've read this a couple of times and I'm struggling to understand your system and issue.

Can you please sketch this up and provide some answers to questions please.

Which pumps are these?
The fire water pumps or some secondary pumps feeding the fire water sump pond? you say the pumps will "draw fire water..." What does "draw" mean? Pump in? or pull the level down so that the water flows? It's unclear to me hence why a diagram or sketch would be very useful

"Since these pumps will always be submerged and primed, and the discharge piping will be water full, how does one remove the trapped air " Where exactly is the trapped air then if the discharge piping is full?? you then say "there will be a large section of piping full of air" - Where? Why does it drain out? ? where does the air come from? Have you no check / non return valves?

Any fire water system needs to be very reliable and able to work without human intervention, opening valves or doing anything other than either pressing a button or turning on a fire hydrant. This system does not seem to be like that. Can you elaborate a bit please?

Without this information we can't see what you can see, but most fire water systems keep the system at positive pressure using a jockey pump. So at some point there is a break between pressurised system and non pressurised. This is usually one or two check / non return valves so that when the pumps start they simply open the non returns and start flowing.

Fire systems are not like normal pumping systems so you can't normally have spill back loops or any requirement for valves to open or close or modulate. Just press the fire button / open the hydrant and the pumps start.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

I thought about asking those same questions, but without any real info, except for the irrational stuff, I know how that usually means pulling too many teeth and never getting what you need to know.

Firewater system full of air? How does that actually work. Wait 20m getting it primed while expelling air? Does the air get blown out of the pipes onto the fire?

What's going on here?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[bizkitgto]

LittleInch - please see my response below, started with a “>>”.

I don’t know how to attach a sketch on my phone, I’ll try later.

*************


Which pumps are these?
The fire water pumps or some secondary pumps feeding the fire water sump pond? you say the pumps will "draw fire water..." What does "draw" mean? Pump in?

>> these are vertical turbine pumps, they are fully submerged in a “fire water sump” below the ground.

>> here is an example of vertical turbine pumps: https://www.pentair.com/en-us/products/business-industry/water-supply-pumps/vertical-turbine-pumps/aurora-vertical-turbine-fire-pump-series-914.html&indexName=prod_pentair_products]LINK[/url]


"Since these pumps will always be submerged and primed, and the discharge piping will be water full, how does one remove the trapped air " Where exactly is the trapped air then if the discharge piping is full?? you then say "there will be a large section of piping full of air" - Where? Why does it drain out? ? where does the air come from? Have you no check / non return valves?

>> the pumps should always be liquid full, as they’re submerged in the fire water sump below grade. The discharge piping is above grade, and has check-valves installed just before connecting to the fire water main header. When the pump stops, any liquid left in the discharge piping between the pump and the check valves will drain back into the pump below grade.

>> the liquid level in the fire water sump will always be below grade, and the pump will always be submerged, however, the liquid level in the sump will be the same level in the discharge of the pump, and that level will always be below grade. When the pump starts, how does that air trapped in the discharge of the pump piping get out of the system?

Does this make more sense? This appears to be a very common setup for firewater systems that pump from a sump below grade.

 

[bizkitgto]

1503-44 - please see my response below:

**********

Firewater system full of air? How does that actually work. Wait 20m getting it primed while expelling air? Does the air get blown out of the pipes onto the fire?

What's going on here?

************

>> these are vertical turbine pumps, they are fully submerged in a fire water sump below grade. When the fire pumps aren’t running there will be a column of air in the discharge piping of the pump all the way to check valves, downstream the check valves the piping will tie into the main firewater main header. When the fire pumps auto-start they will push that column or air into the main fire water header.

This is almost identical to a cooling water system setup where the pumps are submerged in the cooling water basin.

 

[bimr]

The air release valves typically have a regulating device to control the flow of exhaust air to minimize water hammers. These devices are common and carry FM approval.

 

[FMJalink]

Hi bizkitgto,
For me offshore is some time ago. Your setup is basically the same as with offshore platform seawater lift pumps, though most likely with somewhat less flow. To remove the air from the vertical lift pipe an air release valve upstream the check valve is used, as described by bimr above. Your by-pass is used starting up the pump, as you mentioned yourself already. With fire fighting the pump discharge (block) valve normally should open automatically, I think. That will depend on the locally applicable fire code(s) as NFPA etc.

 

[1503-44]

Biz, OK making sense now.

You can post images using the camera icon on this page's tool bar. Click it then browse through your file manager to upload, then click the post button.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

Biz,

Thanks for reply.

This is the key section

"When the pump stops, any liquid left in the discharge piping between the pump and the check valves will drain back into the pump below grade."

why and how does it drain?
Unless the pipiing is about 8m higher than the sump water level, you won't pull a vacuum and unless you deliberately let air in somewhere the water won't drain out.

what most people do is fit a "foot valve" on the inlet into the pump to prevent any draining back.

https://blog.craneengineering.net/what-is-a-foot-valve

FW pumps are normally simple, strong and robust. Even if some air gets into the FW system it will not be a big volume and a bit of air is not worth bothering about and if anything acts as a cushion to prevent surge.

As said previously, NFPA pumps systems at best and only recently I think allow a small recirculation during the weekly 30 minute churn test and are built to not require any manual or electric powered actuators. Previously there was no recirculation and the pumps got rather hot...

You will need to check to see if these spillback / recirculation lines you mention are permitted under NFPA and approved by your AHJ. NFPA specs can be a bit odd so you need to read them carefully or get an approved designer to design it and certify in accordance with the requisite NFPA regualation.

As they will test these weekly you can monitor the discharge piping and vent any air which has appeared or see if there are any strange bangs or vibrations.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[goutam_freelance]

Check valves are rarely 100% leak tight. As at downstream of check valve there will be sustained pressure from jockey pumps, the piping between pump and check valves are expected to remain full due to small leakage across check valves. Even if a small amount of air does remain -as LittleInch said "it will not be a big volume and a bit of air is not worth bothering about".

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[TenPenny]

The normal process with non-FM vertical pumps in an installation like this is to have an air release valve on the discharge head / discharge piping, it's a standard option on most vertical turbine pumps.

I don't know what NFPA (if applicable) says about this, I suggest checking out the applicable code.

FYI - the courts in the US have ruled that if a code, such as NFPA xx, is made part of law, such as being required under a building code, then it must be available at no cost.

 

[LittleInch]

Just go onto the NFPA website, register for free and you can see any of their codes on line for free including past versions.

you just can't download them.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TenPenny]

I got some details wrong:

A federal court of appeal (not the SC, I was wrong) has ruled that if a code or standard is incorporated into law, it cannot be copyrighted.

That certainly has some interesting consequences involving building codes, for example.

 

[1503-44]

You can read it here.

https://www.nfpa.org/codes-and-stan...ds/list-of-codes-and-standards/detail?code=20

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."