Be the water

Mike T., Swampeast MO

...have ZERO experience in industrial and/or cooling towers and won't even BEGIN to go that far on a limb...

WILL say though that reducing the size of a solenoid valve (and/or piping to which it is connected) would INCREASE hammer as velocity would rise given same amount of flow. It's the rapid stop of fluid at high velocity that creates hammer and backflow prevention devices create a "brick wall" against back-pressure as well as flow...

joe_6

Backflow Preventers

Im trying to be the water grasshopper.Could somebody please describe the proper installation of backflow preventers.I am in a commercial building with chillers ,hotwater heat exchangers and such.We have BFP on each system where water can be contaminated.My question is on the makeup for the chillwater system the system is as follows.There is a4inch main domestic line which the makeup for chillwater taps off.It tees off 4inch line,reduced down to 1inch and then there are 2 check vaves then the pressure reducing makeup valve then 14 feet down the line is the BFP,thenit goes into chillwater expansion tank 10 feet farther down line.My question is shouldnt the BFP be installed right off the tap of the 4 inch line and the press. reducing vale come after BFP.Because it seams as it is that the press.now right after the reducing valve and before the BFP could backflow back into the main if main pressure drops below system pressure and check valves do not work.WOW that was alot i hope its understandable.Thanks.

bert

I can think of two points to discuss.
The first being that the use of two separate conventional check valves in series has become a thing of the past, and is not generally accepted as providing true backflow prevention.
The second is location, where almost every mfgr. shows the backflow preventers ahead of or before any pressure reducing valves. It is true they have spring checks, but why not let the additional pressure work for you?

Tom Anderson

Mr. Overman has it correct.

Two check valves in series not acceptable for backflow protection because there is no way to determine if checks are fouled. Very old fashioned. The backflow can go in 1 inch line.... much less expensive than a 4" dia backflow preventer.

The make-up water PRV goes downstream of reduced pressure backflow preventers. This is because the backflow preventers always have a minimum pressure drop. The PRV is there to deliver water at a defined and consistant pressure. It will compensate for backflow pressure drops.

Make up connection to xpansion tank line... make sure xpansion tank connects to suction side of CHW pumps, as close as practical. Never connect makeup water line to discharge side of pumps, else you will have a lot of pressure relief/tripping problems.

Hope this helps.....

Unknown

BFP after the PRV

> I can think of two points to discuss. The first

> being that the use of two separate conventional

> check valves in series has become a thing of the

> past, and is not generally accepted as providing

> true backflow prevention. The second is

> location, where almost every mfgr. shows the

> backflow preventers ahead of or before any

> pressure reducing valves. It is true they have

> spring checks, but why not let the additional

> pressure work for you?

Unknown

BFP after the PRV

If you put a backflow preventer beyond the pressure reducing valve on a system that changes temperature, you can expect the BFP to vent to atmosphere when the water warms up, and the pressure on the outlet of the BFP becomes greater than the fixed pressure between these two devices. I think the preferred way to have these set up is to have the PRV protect the BFP from these changes in pressure by having the BFP first.

If you buy the combo unit of these two devices assembled together, the BFP is first.

Noel

Terry

yup

Particularly since a RP device operates on a reduced pressure principal.

The BFP shall dump when system pressure exceed supply pressure by 1psi. therefore you want the supply pressure high (not reduced), since your system pressure will rise due to thermal expansion.

I've seen PRV's & BFPs put in reverse order and the only ones that didn't dump everytime the boiler fired, were the ones that had the shutoff valve closed, rendering auto makeup useless.

Hope this helps.
Terry

joe_6

Thanks

everybody for responses.Thats what i thought.The BFP should come first then the PRV makeup.This system also needs more pressure gauges on it so i can see whats happening.Asit is now it only has 1 pressure gauge downstream of PRV and before BFP.The problem is downstream on the 4 inch where it comes to an end it reduces down to about 2 inches for cooling tower makeup which has quick opening eletric solonoid valves and when these valves snap open and closed i can see the pressure drop way down then way up on my pressure gauge which is downstream of the PRV but before BFP.The BFP does not vent any water so this tells me that the water inline right before BFP is backflowing thru PRV and check valves when the mainline supply pressure drops because of cooling tower solonoid valves opening.Thanks.

[Deleted User]

Double checks OKay...

Provided there is a testable BFP down stream. It is common and accepted practice to install spring checks prior to a RZP BFP. This keeps the BFP from seeing any flushometer induced pressure drops in the main and eliminates "spitting".

I've used it many times to correct a spitter.

The double czechs must be DIRECTLY before the BFP, no room for any branch connections.

ME

ME

joe_6

Mark

Thanks.The doublechecks should come first where it comes off main then the PRV then the BFP is that correct.I wish i could draw apicture of piping but i dont have capability with computer.Thanks again.

joe_6

Mistake

I meant to say doublechecks come first then BFP then PRV is that correct.

Mike T., Swampeast MO

Not a pretty picture

But believe I incorporated everything said here and included anti-hammer/expansion compensation.

I didn't install anti-hammer devices in my lawn irrigation. Backflow preventer loved to vent when solenoid valves shut. Was impossible to install anti-hammer devices "as close to valve as possible" so one required by mfgr was huge and expensive, so installed a small well bladder tank. It works, but don't know for how long...

joe_6

Damn Mike

Your a regular Mikey Angelo ,thats butyful and just how the system should be except for that anti hammer device we dont have but maybe needed later if water hammer problem is not solved.I think those solonoid 2 inch valve should be reduced way down to maybe 1 inch so pressure drops and hammer are not so violent.Depending on makeup requierments of cooling tower of course.Or we should go to a pneumatic cooling tower makeup valve to stop sudden pressure drops and hammer .Damn im learning,you guys are great.

Art Pittaway

Water Hammer

First look into solinoid valves that are Pilot operated, the opening & closing speed can be adjusted. I haven't looked them up in a while but were available a few years ago, seems they have to be above a certain size.
Art.

joe_6

Speaking of water hammer

after my last post i thought why dont i just install aball valve before or after solonoid and just throttle down on that so when solonoid opens so much water willnot be moving,and less hammer and pressure fluctuations.Thanks Mike.Speaking of water hammer again i see alot of solonoid valves on different water systems in commercial buildings and water hammer is bad ,wonder more pipes dont burst.All things have to be considered when installing a solonoid valve in water line to eliminate hammering.Water pressures,open or closed system,velocity,pipe size,GPM,etc.Thanks again Mike.

Jerry Boulanger

Use a solenoid operated

diaphragm valve to eliminate water hammer. They are slow closing and are available either normally open or normally closed, in sizes from 1" to as big as you want.

Re: make-up water, unless you have packing gland pumps that continuously leak water from a closed system, consider using a packaged system feeder for make-up. No connection to the domestic water supply, you can pre-treat the water, get leak detection, flood protection, and by storing the make-up water in an atmospheric tank you will reduce the entrained air and allow any suspended solids to settle out.

[Deleted User]

Correct...

ME