Help!!! Any ideas

[coolhandlew]

Hi all,
I have a small problem! Last year I installed 4 x 100kw Edpac close control R410a DX systems to a data centre. The pipe run is around 50m, 7/8" liquid, 1 1/8" gas very well supported on bracketwork with cushion clamps approx every 1.2m. Thing is, one of the liquid pipes has moved along the brackets. This has happened along a 25m straight section of the pipework and has stressed the elbow at each end of this stretch. It has actually moved around 120mm. This has happened on only one of the circuits.

At first my theory was that liquid travelling along the liquid line at high velocity was essentially pistoning into the elbow and forcing it through the cushion clamps, the elbow is not a particularly long radius. There are no check valves on the pipework (not in manufacturer spec) so there is some migration of liquid to the condenser. Thing is, even if all the liquid is in the condenser this slug of liquid coming down the pipe should be held up as it compresses the vapour ahead of it.

The next component down line from this is the EEV which I have proved does step fully closed on the off cycle.
The compressor is VSD so it obviously ramps up.
.pipe creep1.jpgpipe creep2.jpgpipe creep3.jpg

Has anyone seen anything like this before??

[Rob White]

.

I have seen liquid hammer knock 7/8" solenoid valves off the end of the pipe.

If you are sure it is liquid and you have to convince your self it is,
do not underestimate the amount of damage liquid will do inside a pipe
especially over a 25 mtr length.

But why only this leg? Why is it not happening on the other runs?

Regards

Rob

.

[Brian_UK]

You say that the EEV is closed in the off cycle, fine, what control does the EEV operate under when the system starts?

Is there a solenoid valve in the liquid line prior to the EEV?

[The Viking]

Hmm, this is also the top pipe of the run, most exposed to the sunlight?
Any chance the temperature variations could be higher on that pipe compared to the others?

Anyhow, on long straight runs it is always good practice to put "stress bends" in, basically U-bends to allow for lateral movement of the pipe regardless of if this is due to liquid hammering or thermal expansion/contraction.

Also worth remembering is that any pipe support will only support in the pipe in one axis so that your pipe is pushed through the cushion clamps is not surprising, that is their design.