What valve to use for low water hammer

Try installing a hydraulic accumulator to absorb the kinetic energy.

& maybe a check valve/ orifice combo in reverse direction? to damp

I use these Sioux Chief water hammer arresters in my plant. I like the hydra-rester, they're simple, they work great, and last.

http://www.siouxchief.com/B_Products_Prods.cfm?ID=35

I've also had good luck with this type of arrestor but this project has a low budget to enable a reasonable payback. I was hoping to find a valve that when operated carefully (by owner) would enable a slow controlled shut off. There's no cost for the water and it all goes back to the same river so it is feasible to install some type of abypass to reduce the flow before complete shut off.

thanks for your input

In this case, why don't you just install a Y to divert the water to the river. After diverting water to the other pass, it will be very easy to isolate the generator from the high pressure of water and it will be very easy to shut off the valve.

cri,

Water hammer or pressure surges are caused by the rapid stoppage of the moving fluid. In order to eliminate or reduce the magnitude of the surges the stoppage should be done slowly. Any valve that can be closed at a variable speed would reduce of eliiminate the surges.

chama2633

this was a good answer: water hammer is due the high stopping speed of the flowing water stream. It is a result of inertia.

The slower you can close the valve, the better.

A gear operated butterfly valve is already a good start.

Globe valves also close very slow.

If you have the money you can start experimenting with those special valves that come out of the agricultural water distribution world. Water hammer is nasty, but don't forget to add a compensator: the rise of the pressure will shorten the pipe. Plastic pipes are known to show this effect very heavily.

Install a pipe tee just ahead of the valve. The third arm of the tee should be a capped vertical pipe of the same diameter as the supply pipe (or larger). The air trapped above the water in the pipe will cushion the impact if the valve is closed too quickly.

At one time, plumbers knew to do this. Maybe some still do.

Same, same....................simple accumulator, as previously mentioned.

Thank you Bubba... I was thinking of the same scheme... and it is cheap and dirty.

Bill

I suggest installing 2 Belimo valves in a "three way" configuration. This will provide an avenue for the water to bypass your generator and not get the water hammer. You could then run another generator during bypass.

bubbapebi: take a look to the document in the Switchman´s post and read "The fallacy of air chamber".

When designing water systems a gate valve is used. This will slowly cut off the water supply so you are less likely to get water hammer. Also a cheap way of making a water shock asorber is to simply install a bigger empty vertical pipe (capped off at the to of course) near the place you want to protect. The air inside will compress and disapate the pressure wave created by water hammer. Of course you can buy a water hammer arrestor from places like this

http://pexsupply.com/Categories.asp?cID=608

Yes it's good to use gate valves!!!!!

I am currently look into a system with three pumps in paralle with two water supply pumps trip while one still running. The soft ware shows a result of when the valve shut of too slow will also cause a reversed flow goes into two tripped pumps.

Do you have such experience in real world?

CRJ:

You want to make an arrangement to shut the valve off very slowly to avoid or at least reduce water hammer. If you can be assured that whoever will shut the water off knows to shut the valve slowly you could use any kind of valve. I have a similar problem with my irrigation system--it is nearly identical to your friend's arrangement: 4" and 230 feet of head. I use ball valves which can be shut off in an instant but I make sure everyone who will use the valves KNOW to shut them off slowly!!!

I'm not sure what a diaphram valve looks like in a 4" size--I have only seen them in small sizes. But I don't think you need a valve that sophisticated (read "expensive")

I would suggest using a butterfly valve--they are dirt cheap--but pay the added expense to get one with a "geared handwheel operator". This is a little worm gearbox that slows down the action of the butterfly so when you crank the handle it will close slowly. Butterfly valves are usually sandwiched between two flanges so you would have to come up with an adapter arrangement to hook to the PVC pipe. I would use a steel flange with 4" threading, and get a PVC adapter to 4" pipe thread.

A simpler arrangement might be to just use a 4" threaded gate valve...as long as the valve is closed slowly things will be just fine.

It is easy to hear when the valve is starting to throttle the flow--this is where you want to take it real easy on the closing.

I bought a 4" geared butterfly valve on eBay, brand new, for well under $100 a year or so ago. You will find lots of them as surplus building fire protection valves.

Hope this helps,

Jon.

Nobody has asked the correct question. What is the head of the tail race? If the water is only dropping 30 ft, one solution would be correct. If it is dropping 300 ft another solution maybe required. There is also an issue of vacuum break. If you should happen across an old hydro-electric plant which employs piping from the pond to the plant, you will see pipe towers at the top the race to prevent race (pipe) suction collapse. This is particularly important when you valve off the race at the top, while the valve at the bottom is open.

Note that the problem mainly arisen due to instantaneously closing valves, or flow stoppage. If the pump slows the flow down to zero in Ts seconds, or if the valve closes in less than Ts seconds, then the system should be analyzed for the possible effects due to water hammer, where Ts = 2 L / c,

where,

L is the characteristic length of the piping system, normally taken as the distance between the pump or valve and its source or sink,

c is the speed of sound in the fluid.

So, any valve fulfilling stopping the fluid in a in time ≥ Ts is acceptable whatever the type of valve.

Also, the methods of protections are : Surge tanks, Air Vessels, Air Injection, and minimizing the elbow-elbow pairs

"He needs a shut off valve ahead of the generator to enabling shutting off the water flow. "

For maintenance? Any gate valve will do provided the maintenance guy knows to crack it open slowly.

If flow needs to be turned on and off on a regular basis, you can minimize the effect on the generator by using a valve downstream of the generator.

what you need is a valve with a bleeder in closed position when valve is at lower end of pen-stock you can make with a ball valve take lock off valve turn handle 180 deg. drill hole as large as possible in side of valve trough one side of ball only turn handle back 180 deg. replace lock , now when in closed position water will flow out hole on side attach a pipe to hole side of valve to take up water (glue if valve plastic braze or weld if metal )