3 replies to this topic

[splendid.ye]

Dear Forum members,

 

Based on my experience on the centrifugal compressors, non-slam type of check valve is always applied to discharge line of the centrifugal compressor. 

Here are my questions

 

1. why do we need to apply this type of check valve on the centri. compressor discharge? one thing I can think of is slamming sound when it is closed after compressor shut down. Is there any other reason? or does any one have experience not to apply non slam type and have no problem at all?

 

2. what about reciprocation compressor discharge?

 

3. Are there any other places where application of non-slam type of check valves is remmended or mandatory?

 

Thanks in advance

Edited by splendid.ye, 15 February 2017 - 07:40 PM.

[Art Montemayor]

Splendid:

 

Check valves are installed on the discharge line of centrifugal compressors (and also reciprocating types) in order to avoid any back flow when the compressors are down or being started back up.  The non-slam type is particularly suited to this application - especially as it pertains to the reciprocating type.  However, one feature of this type is that springs are employed in its design - a feature I absolutely detest when applied to pulsating or varying flows.  What type of non-slam valve are you referring to?  There are a lot of different designs and you shouldn't be lazy and just generalize.  You can easily post pictures or drawings of the specific type(s) you mean as I do in the attached photos.

 

Don't forget that a reciprocating compressor inherently has to have a check valve in its mechanical design.  Otherwise, it couldn't compress any fluid.  The check valve that is used is called a "discharge valve" when incorporated in the compressor.

 

 Duo-Chek type Non-Slam Check Valve.JPG   20.93KB   11 downloads

 

 Nozzle-type Non-Slam Check Valve.JPG   63.65KB   10 downloads

[splendid.ye]

Art Motemayor

 

Thanks for your reply,

 

I have normally applied dual plate type check valve as non-slam check valve as also shown in the picture you attached.

The thing is when check valve is used to avoid back flow when compressor are down, why do we need to apply especially non slam type?

I assume that other type of check valves are also able to prevent back flow not just non-slam type.(Check valves are meant to be)

Is there any specail reason for that?

 

And also for reciprocating compressor, like you said, it has discharge check valve in its mechanical design, even though it has one in its mechanical design, do we still need on on the discharge line? casuse I have seen it in my previous projects but not non-slam type.

and shoul it be non-slam type as well?

 

lastly, have you seen any place where non-slam type of check valve is used in the process line not just discharge line of rotating equipment?

 

Thanks in advance

 

[Poosticks]

When the compressor shuts down the pressure will be lost at the outlet of the compressor and the downstream gas will flow back.

A standard check valve will allow a considerable volume to pass back (as the valve will take a while to close). A non-slam valve will close rapidly and hold the downstream pressure. [The 'non-slam'  isn't specified for its ability to stop slamming - it is just its quick closure].

 

The nozzle non-slam valves are better as they are 'true' non-slam. Dual Plate style may be advertised as non-slam but realistically the performance is far inferior - it benefits from a spring but most of the closure force comes from the gas back-pressure.

 

I personally would not specify a separate 'non-slam' valve on the discharge of a reciprocating compressor. As has been mentioned - the compressor will have an integral valve which will be sufficient.

 

 

Non-Slam check valves are so-called 'high integrity' check valves so they also find applications on well-heads; they can be used at the end of lines before mixing (no need for non-slam).  In compressor applications they are also used on the suction side of multi-stage units... in the event of plant trip the inter-stage pressures will be maintained.

 

 

Just as a footnote - It is critical that the discharge check valve is installed immediately after the anti-surge take off. Quite often the valve is installed downstream of the heat exchanger which can make the valve less effective (the valve will only 'check' the volume downstream').

 

I hope this makes sense (i'm writing very late at night )