Spool piece required between check and gate valve?

[DGrayPPD]

Refer to link. This is just a general question. Notice in the image, the check valve and block valve are bolted together with a note stating to tap the check valve when approved by client specifications, otherwise use a spool piece with a bleed valve. I understand that client specs dictate the proper arrangement, but whenever the specs do not indicate which method they prefer, what is the most economic and practical method to use? My three scenarios are:

1) Bolt check valve to block valve and tap check valve to allow draining and relieving pressure between valves as shown in the image.

2) Add a spool piece between the valves with a bleed as noted in the image.

3) And my third scenario I am curious about, is would it be practical to use a bleed ring with a bleed valve between the check and gate valve? My thinking is that this would save on the time and effort required to tap the check valve, and save on the cost of adding a spool piece. However I am not sure if this is a practical or economic idea. Would there be any issues to worry about with using a bleed ring between valves?

What makes the most sense from a time, effort, cost, and practicality standpoint?

Thanks for all responses.

http://1.bp.blogspot.com/-v5-w08PFN...+TOP+DISCHARGE+PUMPS+%28API+PUMPS+ONLY%29.jpg

 

[BigInch]

Now you've gone and opened a can of worms.
You can searh Eng-Tips. Try "check and block valve"

Reaction to change doesn't stop it

 

[DGrayPPD]

I understand the varying opinions on whether it should be pump/check/block or pump/block/check, however my question is only pertaining to the pump/check/block layout. If this is the preferred layout, which scenario of the 3 above makes the most sense for relieving the pressure?

Thanks

 

[pennpiper]

DGrayPPD,
Your Option 3 is the most cost effective.

Sometimes its possible to do all the right things and still get bad results

 

[DGrayPPD]

Does that make it the best option of the 3?

 

[BigInch]

No. Best technical option depends on if you want to make pump maintenance easy, or ...
if you think you will have more trouble with broken check valves. A lot of people (I'm not one) seem to think check valve repair is highly desirable.

Reaction to change doesn't stop it

 

[DGrayPPD]

I understand your point, however every piece of literature I have ever read recommends pump/check/block and to me it doesn't seem like as big of a deal to add a bleed ring between the two and just drain off the smaller amount of inventory as opposed to pump/block/check with a drain downstream of a check and potentially draining a larger amount of inventory. That is just my opinion though and I am not stating that your opinion is wrong. Everyone has their own opinion which is great because it allows people to think about things in a way they may not have before.

 

[BigInch]

No problem for me. I buy good check valves.

Reaction to change doesn't stop it

 

[LittleInch]

I'm not getting into that argument again. ....

Why don't you just tap the flange like an orifice flange?? You're not really draing it just relieving any built up pressure if you take the pump out.

BTW your drawing has the temporary stainer the wrong way round. IMHO.

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

 

[rconner]

[also

http://www.eng-tips.com/viewthread.cfm?qid=262461

]

 

[DGrayPPD]

The drawing was just pulled off google, however I do believe the temporary strainer is correctly oriented. Having the point face into the flow allows debris to collect around the outer edge rather than the center. Enough build up in the center could cause pressure drop and plug the strainer. The outer rim is also mechanically stronger than the mesh or perforated center. However what I don't agree with is having it directly on the suction nozzle. There's should be 5-10 diameters free of any obstruction before the auction nozzle.

 

[Gator]

BTW your drawing has the temporary stainer the wrong way round. IMHO.

What?

 

[BigInch]

Strainer is correct as it is.

Reaction to change doesn't stop it

 

[LittleInch]

As I said, IMHO, the stainer obtain end should be pointing in flow direction and inserted at the other end of the spoil. That way the material is in tension and won't buckle and when you withdraw it all the crud stays inside not in the bottom of the spool piece.

I loathe strainers like this as getting them off makes the pump alignment go to pot and takes forever to get right again. Just inset a Y stainer then take our the basket.

Somewhat off topic. What about the orifice flange idea?

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

 

[DGrayPPD]

Bleed rings are cheaper and easier to install than orifice flanges.

http://www.piping-designer.com/inde.../pipe-fittings/95-bleed-ring?title=Bleed_Ring

 

[LittleInch]

I'll take your word for it - can't work out why, but go for it

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

 

[BigInch]

Captured debrie collects in center, produces large head loss, may plug. High pressure force may break up the strainer which all the junk gets taken into pump or compressor. Should not be used except in very low laminar flow velocities if at all. I'm surprised to even find it on Piping Designer's Web Site.

By far the best,

http://www.piping-designer.com/inde...3-temporary-strainer?title=Temporary_Strainer

Reaction to change doesn't stop it

 

[Krausen]

One other thing to consider if bolting check valves directly to block valves is if standard studs/nuts can be used to install. Some block valve types (especially in larger sizes) will have tapped blind holes for fastening. Bolting these types of valves back-to-back with another valve can be tough on maintenance folks if they ever need to disassemble, i.e. studs may need to be cut to pull either valve.

This problem is easily solved by adding a small spool between the valves, which would be the conservative direction I'd lean. Again, this is more of a big bore piping issue. If these are smaller sized valves this may not apply.

 

[Gator]

The tapped blind holes are often related to the diameter of the stem and the bolt hole spacing on wafer style valves. Sometimes you need a combination of cap screws and studbolts.

And of course everybody checks(!) for possible disk interferences if using wafer style checks and butterfly valves near each other (especially for large bore), right?