Silent Check Valve (Yes or No)? 1

[jpwren]

I have an 8" check valve that I need to replace that is in the vertical plane 11" from the discharge of a 1435 gpm pump. We have replaced one in the past with another swing type check valve and it now makes the awfullest beating and banging noise when the pump is running. Since the swing check valve relies on gravity (weight of disk) to shut off, I believe that sudden surges in flow is causing the disk to relax and slam back against the inside of the valve since 1435 gpm of water discharged from a pump is pretty turbulent. I don't believe we have a water hammer problem, but I could be wrong. What I'm looking at replacing the current valve with is an APCO Series 600 Globe Style Silent Check Valve. To fit in place of our existing valve we would have to add a 9 3/8" spool piece giving a possible distance of 20 3/8" from the pump discharge to the check valve.

Now my questions: Does anyone think that the silent check valve is not a good idea in my situation? Can someone give me any pros and cons by going with a silent check valve? I have my own, but I'd like to see what others have to say. Any other advice is also welcomed.

P.S.> I have to be able to get this valve no later than 3.5 weeks from now.

 

[TBP]

Crane's Technical Paper No. 410 has information on check valves. They need to be sized for the flow conditions. Check valves are a lot like control valves - they're usually one pipe size smaller than the correctly sized line in which they're installed.

Over-sized check valves never fully open, and the discs flap like flags in the wind. This is the prime cause of these valves wearing out before their time. A check that's over-sized, never fully opening, will typically have a larger pressure drop than a smaller, properly sized valve that opens right up.

 

[smckennz]

Your swing check is too probably too large for the flow/pipe size.
Your line velocity is around 1.9 m/s. You want at least 2.4m/s to open the disc fully for a conventional design swing check.I assume you are pumping water If you have an external spindle, installing an arm and a spring (acting in the closed direction) will help at the expense of wasting power.
Wafer type check valves work OK and are cheap and easy to fit, but the springs eventually break and water hammer ratings are not that brilliant.

Cheers

Steve

 

[imok2]

smckennz, according to my calcs I get the following:

These are the results:
velocity ft per second: 9.2033
Reynold's Number: 567830.2229
friction factor fa: 0.0156
friction factor f: 0.0155
head loss ft: 3.0647
pressure loss psi: 1.3280
or 2.8m/s Just curious where you got 1.9m/s
I do agree with you and tbp on the ck valve being oversized,however.

 

[PAN]

imok2,
I agree with you that line velocity is 9.2 fps (2.8 m/s). However, it is more than 2.4 m/s (from smckennz's comment). Why do you still think that check valve is oversized? Please advise me.

 

[PUMPDESIGNER]

Silent checks can quiet down the hammering, but they are often vulnerable to small particles in the pumpage, makes them stick open, many of us in the pump industry avoid them on discharge of pump because of this.

Many use a split disc type check. Pretty good against hammer or to quiet the system down, much less vulnerable to sticking like silent checks. Again however, springs go away in time.

PUMPDESIGNER

 

[smckennz]

Oops
you are right; 1.9m/s is your flow for a 10" line.
I would normally expect 2.8m/s to be sufficient to hold a conventional swing check open. However if you have a low Cv model the full disc lift flow may be higher. For example U/L rated swings are rated by crane to require 3.8m/s on water.
Like pumpdesigner, I dont like centerpost guided check valves lile the Apco600 unless the water/fluid is really clean.
Have a look at the Keystone Fig 86. They are a sprung wafer swing check (sort of). Cheap, with rubber seat and the spring. at 8" the full open steady flow velocity is only 1.5m/s. Normally available off the shelf. I have used heaps and wrecked only one, due to surge prevention system failure, not the fault of the valve.
When fitting be careful that there is plenty of clearance between the open disc and the makeup pipe as the disc opens into the pipe.

Cheers

Steve

 

[stanier]

I have replaced swing check and dual disc check valves with Noreva silent check valves and have found that the waterhammer noise is mitigated. This has been on power station water supply or water treatment plants.

For wastewater of slurry service you might consider the Red Valve "duckbill" type of non return valve. This also assists in surge effects mitigation.

The silent check valve is preferred over swing checks with counterweights, dampeners, pilots, bypasses etc. There are far fewer moving parts and less for people to fiddle with in the field.

Be careful of the Far East copies as they are one or two prototypes behind the modern multispring metal seated silent check valves as available from Noreva or Mokveld.

For the theory refer to Fluid Transients in Pipeline Systems By Thorley. The 2nd Edition has just been published and is available from:-

Orders Department
Professional Engineering Publishing Ltd
Northgate Avenue
Bury St Edmunds
Suffolk
IP32 6BW
England

Tele: (44) 01284-724384
Fax: (44) 01284-762069
e.mail orders@pepublishing.com

The check valve should really be selected, installed and maintained with the same level of engineering as a relief valve. Its effect on a system may be as catastrophic as a non performing relief valve.

 

[jpwren]

Where can I find the Keystone Fig 86? I've done a few searches and can't come up with anything. Is there a website where I can look at them or a distributor that I can speak with. Also, how do I determine the required line velocity to hold open different swing type check valves?

The new valve will be in a raw water system directly after a duplex strainer, but we all know that they're not going to catch 100% of the particles that go through them. Therefore I'm now a little leary of going with a centerpost guided check valve like the Apco 600. Thanks for all the help, I've really learned a lot.

 

[stanier]

Keystone valves can be found on the Tyco Flow Control website. But beware it was these valve sthat I replaced with the Noreva silent check valves.

 

[smckennz]

I can see I wont win a trick on this one.
Stanier, how did the Keystone check valves fail?
Stuck spindle, hammered out disc?
What was the service? High lift low friction?
Every so often I find something cheap that works, and the Fig 86 appeared to be one of these; two methods of zero flow disc return (spring plus gravity),resilient seat, a sensibly profiled disc, and a good price. Not mad about the bushing arrangement or the large opening angle. I have used them where I shouldnt (grit laden water) because of time constraints, and they have worked better than expectation. The spool pieces I included to enable retrofitting elastomer ball checks are still in place after 3 years.
However if the Fig 86 has some specific shortcomings, I would like to know.
There is a lot of negative press about the humble swing check; I have found then OK in many applications, and they have been around for over 100 years so there must be something going for them. By far the biggest problem is oversizing so the disc doesnt stay fully open. This is one feature they share in common with control valves.
Guess I had better think about crossing the Fig 86 off the"cheap but good" list and moving them into the ??? list along with a number of guided post (silent)check valves.

Cheers

Steve

 

[jpwren]

After much deliberation and a lot of help from this discussion I think I am going to go back in with a slanting disk check valve such as the Crane Fig. 24 or the Apco Series 800. A brief description about the Apco valve can be found here:

http://www.apcovalves.com/compare3.htm

It seems to be the best of both worlds when compared to conventional check valves and silent check valves. Anybody have one of these in service anywhere and if so how does it perform?

 

[PUMPDESIGNER]

Although we do not use the apco brand, we use these all the time. From our perspective the following applies:

1 This type valve is reliable in function due to its simplicity, large clearances in the operating mechanism.

2 Resists failure due to particles and also from deposits of minerals.

3 Very good for separating pumps where the only real function is to stop circulation between pumps and a small amount of leakage is acceptable.

4 Not good for solving hammer problems, too slow.

PUMPDESIGNER

 

[stanier]

The system had a high head. A common line was used to feed a reservoir and also served as the main to the township. When the pumps stopped there was a flow reversal that caused a pressure surge. The check valves slammed closed and the piping suffered severe vibration.

Thye problem with a swing check valve is the geometry. The hinge point at one edge of the disc means that the disc has a long travel before closure. Whereas the silent check valve has a short distance. Therefore the disc in the swing check was at a high velocity caused by the high reverse velocity of the water column. This energy was released in the form of noise and movement of the piping.

For this reason tilt check valves are superior to swing check and nozzle type valves are superior to both.


ARD Thorley is one of the leaders in this field and the recently re published book mentioned above is a must for engineers in this field.

 

[PUMPDESIGNER]

That Apco link was good, very good.
I like their stuff.

PUMPDESIGNER

 

[PAN]

All members,
If we install a hydraulic accumulator in the piping system at discharge of pump, can we still use swing check valve without change to silent check valve? Please comment.

jpwren,
I understand that you decide to change to slanting disc check instead of swing check (single disc).Will you also decrease the size of check valve to less than 8"?

 

[jpwren]

PAN,
No, I will keep an 8" valve there because the slanting disk check has such a short opening distance and only requires a slight pressure differential to fully open. Because of these features I don't believe the disk will be "flapping like a flag in the wind" like an oversized conventional check valve. Another major reason for not modifying the current design of the system is because of tight time constraints to get the unit back in operation as soon as possible.