Check valve with perforated disc

[alienitmeca]

Hello,

I am currently working on a water pumping station with an overall capacity of 2200 l/s (nearly 8000 m3/h), the latter is delivering water to a storage tank. The scope of the project includs installing surge tanks to protect the system from water hammer effects. According to the client specification, a check valve ,with a perforated disc, must be installed in the line entering the surge tank. My inquiry is as follows:

The surge tanks protects the piping system along with other equipements by letting the water flows in and out of it. So, it would be pointless to install a check valve in the piping that feeds it, So:

- What special featers does the perforeted disc of a check valve has ?

- How could we set the specification of the holes to be perforated on the disc (size, number and arrangement)

- Should the check valve be installed towards the surge tank or is it in the opposit direction ?

This the first time I encouter such design, so all informations, recommendations and ideas will be very helpful

Thank you

 

[LittleInch]

Its a little difficult to work out your system without a drawing or a sketch, and "must be" is usually where someone simply doesn't understand a system or it was like that on the only one he's ever seen before...

Perforated check valves are used when you want a simple system which allows flow in one direction with minimal pressure drop but reduced flow in the reverse direction with a lot of pressure drop.

Sizing of the hole is basically an orifice calculation - you know pressure one side, pressure the other and the hole size dictates the flow.

I can only think that where you have a pressurised surge tank / accumulator you need unrestricted flow into the tank to relieve the surge flow, but you don't want unrestricted flow back out creating another surge, but you do need to slowly release the volume / pressure in the surge vessel. This only really applies to pressurised vessels. the key word is slowly release the surge volume.

All depends whether your surge is at the reception end ( usually a positive surge pressure) or at the pump end ( usually a negative surge). You tell me I don't know.

Doing this with a check valve is not great engineering as check valves fail regularly but I guess it depends how often you get or anticipate surge events occurring. If its every time you start / stop then you need something more robust, if its an accidental case once every 10 years then it's a different case.

Draw or sketch your system so we can understand where the tanks are, what types of tanks and where this check valve "must be" installed.

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

 

[BigInch]

Sounds like they want to surge into (direction of the check valve) the tank, then reduce the force on the check valve by allowing some pressure to bleed through that hole, as it closes back against the seal after the surge stops. Sometimes that force is enough to shatter a swing-type check valve clapper.

 

[alienitmeca]

Please find attached a sketch for the pumping station indicating flow direction, check valve position and arrangment of pumps piping and surge tanks,

As it is indicated on the sketch, surge tanks are at the discharge line of the pumps.

I hope this helps clarfying the situation.

 

[bimr]

For a system of this capacity, you should definitely do a surge analysis.

http://www.swawwa.org/ace14presenta..._Pumping_and_Distribution_Systems_Crowley.pdf

" By partially limiting or blocking the action of the check valve, either through by-passing the valve with a smaller diameter parallel line or by perforating the valve itself with a relief-valve-like opening, a portion of the high pressure fluid can be passed back to the relatively lower pressure side, thus bringing the two sides into closer hydraulic communication, and limiting the upsurge on the downstream side."

https://digital.library.adelaide.edu.au/dspace/bitstream/2440/41998/2/hdl_41998.pdf

It is not typical practice use perforated check valves where I practice. It would be preferred to design the system to eliminate the water hammer using techniques such as soft start controls, quick closing check valves, etc.

 

[BigInch]

I can second that. The hole in the clapper is a poor boy's substitute for the real thing, which on a major liquid pipeline is typically one of these,

http://www2.emersonprocess.com/siteadmincenter/PM Daniel Documents/Surge Relief Valves.pdf

http://www.spxflow.com/en/mj-valve/pd-mp-ctlvalve-axial-surge-relief-danflo/

 

[LittleInch]

I agree it's not great but water systems like this tend to be a bit brutal. At that location I can only assume these are pressurised vessels. Only a transient analysis can tell you whether the problem is a high pressure pulse from the far end or a negative pressure pulse caused by sudden stop of the pumps. This will dictate whether you need a valve like this or which direction it is. My guess is that it is a negative pulse and hence flow out fromthetanks is the critical direction, but it is only a guess.

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

 

[BigInch]

Then why would you need a check valve for a negative pressure surge, or for a negative pressure wave it might even be preferable to reverse the direction of the check, from tank to mainline, rather than from mainline into the tank. I think the hole is only to reduce the closure force on the clapper. If the hole is small, I think that would be definitely true. If the hole is specified to be relatively large, then I would question why a check valve is needed.

 

[LittleInch]

I don't know. I can only speculate that they want to try and avoid too much fluid flowing one way and then another.

For reasons we don't know the client seems to want one. Probably in error, but we don't know.

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

 

[BigInch]

If the tank's fluid surface level was slightly higher than the tank's inlet at normal pressure, maybe the tank would drain back into the line through the hole when the pressure reduced, then it would be ready for another surge.

 

[georgeverghese]

The perforation on this check valve just upstream of the surge tanks would eliminate the surge event that would occur during a power failure when all pumps coast to a stop and reverse flow occurs momentarily. The pressure wave would bounce off the slammed shut check valves on each pump, but wouldnt get the chance to cause the surge due to the wave dissipation through the perforation.

A damped check valve would work just as well.

Presume this check valve is on a horizontal piping run, else there would be flow turndown issues with a dual plate check valve. Would guess a 3mm hole on one or both plates would be okay.

The Daniel surge relief valves suggested may act as ultimate protection in case there is a risk of plugging on one or both of these perforations.

Guess the only reason for this perforated check valve would be to minimise the hazard from a reverse flow from the pressurised (or elevated) large surge storage tank(s). What is the total volume of these surge tanks, and at what pressure (or elevation relative to pump grade) are they?