Swing check w/ screwed(?) relief valve...

[dgsbsme]

I've come across a swing check in the discharge (vertical) of a Liquid Ammonia pump (-28°F) that has a relief valve coming out of the body of the check valve. Can't see exactly how/where due to insulation, but I expect it is coming out from a threaded boss on the check body. I assume it is on the downstream side of the check (when check is closed) and probably for thermal relief.
Why not on pipe instead of Check body? Is there some special reason for locating it on the check body?

The client only knows that it was originally designed by M W Kellogg that way (45 years ago) and they know it works that way so they want to duplicate it on our new (increased capacity) pump installation.

Hoping someone out there has some intimate experience with this type arrangement.
-dgs

 

[LittleInch]

The only thing I can think of is that the valve supplier / designer wanted to be able to pressure test the valve in its position without adding another connection, but it is pretty strange in my view to do this when you could do it much easier on the pipe.

Without a drawing or a photo there are few too many "probablies" and assumptions in your post for my liking. Unless you know for certain that it is a boss connecting directly to the chamber then you are speculating as much as I am.

Maybe they just wanted to save on insulation - who knows?

questions - Are you absolutely sure it's a swing check - some other types can look like it and are you sure this tapping isn't something to do with it being vertically mounted?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[dgsbsme]

The P&ID shows the Relief Valve coming from the Check Valve. Symbol indicates Swing Check.
The attached photo shows the Relief coming off directly opposite the bolted cover.
It is a very short relief run, from Discharge directly to Suction line to Pump. Both Suction and Discharge are vertical lines.

 

[racookpe1978]

A swing-check valve in a vertical run of pipe?

Look again.

Now remember, IT DOES NOT MATTER WHAT THE P&ID SHOWS.

What is actually installed in the field (now at least) is what matters. Pull the insulation. Retrace the lines by hand, double-checking what you "think" you found before, against what is actually present. Check relief valve settings by label and design and direction. ANYTHING that can be built can be built dead wrong.

Just the fact that the plant is operating now does not mean it is operating safely nor efficiently as originally designed, but it also means that is IS operating. Somehow.

So figure out WHAT IS PRESENT.