valve check selection 7

[jorgefherrero]

I have to select check valves for high pressure pipes (70 bar = 1000 psi), for sizes between 2" and 6". Up to now we are using single check valves, but I suppose it may be better to use double check instead, since they should make a slighter water hammer, and probably less pressure drop also. Is this supposition right? Is there a better option?

Thanks in advance

Regards

 

[BigInch]

Save your money.

Although two checks may be desireable for double protection from contamination during a flow reversal, checks do not help water hammer in the forward direction at all and do little to prevent a water hammer pressure wave from transversing in the reverse direction. The main pressure wave is extremely fast moving and usually passes the check before it can close. You may catch a reduced pressure secondary reflection, but by then any damage would have already happened.

http://virtualpipeline.spaces.msn.com

 

[stanier]

On a desalination plant in Australia we are using Noreva non slam check valves at this pressure. They have been used successfully on this service for years.

The energy recovery units (DWEER) use them. Check out the Calder website to see them working continuously in these devices.

We have DN500 on the high pressure pumps whose stalled head is 75bar.

http://www.noreva.de

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[jorgefherrero]

Thanks a lot for your comments
Jorge

 

[jorgefherrero]

Hi, Biginch, I think my firrst post led you to confusion. When I wrote "double check" I meant a "double disc" valve, also with two half-circle swing dics, instead of one single swing disc.

Regards,

 

[BigInch]

Right, I thought it was two valves you were considering. I haven't used 2-in-1, but I doubt they do much good for water hammer mitigation, unless they can act inside a few milliseconds. Any comments?

http://virtualpipeline.spaces.msn.com

 

[jorgefherrero]

Thanks, Biginch. I have read of the double-disc valve being fast-closing, but probably it is not enough "fast closing" to avoid the water hammer.

 

[gerhardl]

Jorgefherrero,

In addition to answers already given, please allow me to add :

Noreva and similar types of 'non-slam nozzle check valves ' are doing a good job at preventing water hammer by pump shutdown. The reason is that they are spring loaded and hydrodynamically adapted to gradually close when pump pressure declines, and designed to be closed already slightly before the moment the pressure each side of the valve is equal.

Other types of check valves will in larger degree have a more pronounced (longer)reaction time. With a 'long' reaction time the resulting force or impuls when the valve finally closes will be larger. The shorter the closing time, the sooner the (non compressible? - you say water hammer?) fluid will be contained in a (often closed) vessel/pipeline -without further outside forces giving pressure waves or shocks.

Best selection: hydrodynamically non slam nozzle check valves, spring closed (Noreva - or Erhard for drinking water services/limited pressures) - f available and suitable for your application.

Your suggestion of double disc check valve (spring loaded) as better than a single hinged (weak or none spring) are in theory correct. For your pressure and sizes I would, however, in stead advice you to look into Gestra DISCO types (Flowserve), spring closing, parallell guided high-performance disck check valves. Useed offshore and for process plants for years with good resluts.

http://www.gestra.de

or for US

http://www.gestra.de/~gestra_usa/public_html/

To avoid water hammer by start up, only two ways open:
soft start of pumps and/or good and correct de-aeration of
pipelines of vessels.

Faulty pipeline design may also add to start up water-hammer, including wrong sizing and selection of check valves. Worst cases (opening and closing water hammer): gravity-depending ball-check (and others gravity depending)check valves too large selected. Next worst case: Simple constructed single flap valves when not suited and correctly adapted to total actual process situation.

 

[jorgefherrero]

Thanks, gerhardl, I will have a look at the Gestra Disco valve too.
Regards

 

[BigInch]

The typical methods to migigate water hammer would be to soft start pumps and make sure there is no vapor space or column separation happening. Those methods work with or without a check valve.

To verify the check valve is actually effective in mitigation of water hammer, please provide time to close at various forward flowrates with a complete flow reversal. Alternatively, K with position (K/dS) and the rate of closure with differential pressure, or in other words, the change in K, vs rate of change in pressure drop vs dP, dK/(dP/dT).

http://virtualpipeline.spaces.msn.com

 

[Machiel]

Indeed non-slam check valves are the preferred choice for critical pump applications.

To minimize water hammer (joukowski pressure rise) the supplier should determine the optimum spring for minimum closing time and backflow. For this you should provide him with minimum, normal and maximum flow rate and the expected flow deceleration.

Also Mokveld (

http://www.mokveld.com)

and Stockham (via

http://www.craneflow.com)

manufacture this type of non-slam check valves.

 

[stanier]

For a coverage of these issues get hold of the bible. Fluid Transients in Pipeline Systems by ARD Thorley. The author did a lot of test work on check valves at Delft laboratories.

After reading this you wouldnt use anything but a non slam valve.

Be careful of non slam valves > 10" with a mushroom head. The mass of the head, if the valve is in the horizontal position, can be enough to allow a large gap between bearing and shaft. It has been known for these to jam and cause problems. My preference is for the annulus type with a larger bearing area.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[11echo]

Have you consider a "stop check valve"? it's a not non-slam check valve but has the added advange of being used as a block valve too.

 

[jorgefherrero]

I do not know what a stop check valve is. Can you please explain me?

Regards

 

[11echo]

A stop check is basically a combination of a globe valve and a piston type check valve. It has a stem and handwheel like a globe, but they are NOT directly attached to the "gate/piston", so the piston can act as a normal check valve. But if you want to get a "bubble tight" closure, you crank down on the handwheel and the stem pushes the piston down and closes the valve. I've used them afew times where we want to save money & get the "bubble tight" closure. Check out this link, it shows a section cut thru the valve and may explain it's operation better then I did. Good Luck!

http://www.tpub.com/content/construction/14265/css/14265_126.htm

 

[jorgefherrero]

This may be a very good solution. Thanks!

 

[levins]

also try Goodwin International as they offer the dual plate and are now able to offer the Axial "Non Slam"

http://www.checkvalves.com

 

[CWFCNuclear]

If the waterhammer you are trying to mitigate if being generated by the slamming of check valves at the pump discharge, a Nozzle Check (medium strength spring) will reduce the magnitude of pressure surge by at least a factor of ten compared to a swing check. The spring sizing, disc geometry and stroke length all contribute to the pressure surge. The original Nozzle Check was designed by Mannesmann Demag company and is the valve discussed in the ARD Thorley article that was mentioned in the Stanier post. This product line has been sold numerous times and is currently being manufactured by Cameron (Entech brand). If this valve is needed for a nuclear plant, it is manufactured by Enertech.