Rules of branching pipes from/to cooling water header 3

[danijel999]

If anybody can direct me or explain rules, or advantages and disadvantages for branching pipes from MCW header. The problem is related to cooling water header on the piperack with many taking and returning branches( closed coolimg water systems). Take water from above part of header or bottom, same doubt for returning, and also position of isolating valves, close to place of branching or doesn't matter. I show lot's of examples, but can't find solid reasons for it. Thanks in advance. Regards

 

[pennpiper]

The question is related to cooling water header on the pipe rack with many branches.
a) Take water from top or bottom of supply header? It does not matter

b) Same question for return header? It does not matter

c) What is the recommended position of isolating valves
- close to the user?
or
- close to the header?
or
- doesn't matter? It does not matter

What matters is, what locations provide the best access to the valves for operation?

prognosis: Lead or Lag

 

[danijel999]

Thanks for quick answer.
What bothers me further, regarding place of isolating valve.
Usually we have no heat tracing on CCW ( branching pipes from MCW header)and if we put an isolating valve close to user (heat exchanger e.g.),
and when this part of cooling circuit is out of operation, we have long dead leg, from header till isolating valve, which is going to be frozen after some time.
But, this is solved by putting 2 isolating valves, one close to header, and other close to utility point. Am I right?

 

[LittleInch]

I assume you are talking about two headers - one flowing, one return?? It's a bit strange to have flow and return into one header...

Pennpiper is essentially correct, but IMO this assume you have very clean fluid..

In general taking connections out down can lead to debris (there's always some...) collecting in a connection on low / no flow in that connection and damaging valves and equipment. This is especially imporatnat where standby equipment (e.g. pumps) may be isolated for long periods. Many valves and pumps have failed due to a build up of "crud" in a down header connection. Flow off the top clearly risks any air bubbles going that way or collecting there also. Some valves don't like being in vertical legs, especially non return valves.

Depends on your piping set-up , but often valves close to the header avoid dead legs of hot / cold water. My defalt is always to locate valves close to the header if I have the room, but avoid excessive dead legs or connections from the bottom of the header in these instances.

Your dead leg question will occur regardless of where you put your valve (unless your CCW supply is less than zero C) and putting two valves simply increases the chance of pressure build up in between two closed valves. Trace heating for frost protection (5 - 10 C self limiting tape) is your only solution unless you can have some sort of small return flow to avoid having a dead leg in the first place. You haven't given us enough info to comment properly on this one.

Most of this is simply experience of your particualr industry and seeing what is common / good practice and what can happen when it isn't perfect. HVAC piping is often crammed into a small space which limits your ability to do some of this and often has headers running at high level, but this is my advice.

My motto: Learn something new every day

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

 

[danijel999]

I have 2 headers, supply and return, from which I take and return cooling water.
You have guessed my doubts.
I usually take water of header from above, to avoid pulling impurities from header ( just as you said), but also have to put vent on this section for
hydrotest.
I was thinking to take also from bottom, when I have filter in front of equipment and also, when sometime it's limited space above header. Routing is also cheaper because of avoiding vents.

Thanks for nice answer