Liquid Hammer

[garet]

Hi All,

The company I work for has recently installed a multiplex plant consisting of 2 x 100kW medium temp and 1 x 36kw low temp (for a mini market). This is the first job of this magnitude where we have gone with electronic expansion valves (not the motorised type).

The problem we are experiencing is a great amount of liquid hammer, which has never been the case before. My question is, is there a general tendendancy for liquid hammer with the electronic expansion valves, maybe due to the more frequent opening and closing of the valves? What is everybody elses experience with electronic expansion valves an liquid hammer?

Any advise is most appreciated.

[taz24]

What make are the valves?
Where are they in relation to the evap?
And is there any form of solenoid valve on the liquid line before the electronic ones? If so how far away from the valve are they?

Liquid hamer in normaly caused when a valve opens and the liquid runs till it hits somthing solid like an elbow or a valve.

If the valves are pulsation valves they sould not cause hammer so you need to look to the liquid line and any controling valves in that.

If you have hammer does the system pump down the cases individualy?


All the best

coolrunnings.

.

[Eeram]

Liquid hammering (pulsating) could occur in electronic expansion valve systems, like the Danfoss Adap Kool systems.

Standard practises should be followed in securring all liquid lines tightly on brackets, clamps, etc and to make some form of expansion just before the electronic valve.

Remember, electronic valves can pulse every second, where normal solenoid valves can open and close every 10 to 15 minutes.

I hope this will answer your question/point.

[Silhouette]

Hi Garet,
If by "liquid hammer" you mean the liquid line bouncing, then with any type of solenoid valve you will get movement when the valve opens but it is more apparent with electronic solenoid operated expansion valves such as Danfoss AKV's because they operate more frequently, up to once every second.
The obvious answer is to make sure that any pipework is properly secured, although most supermarkets in the UK just rest the pipework on a cushioned bracket and they all use AKV's!

[DEVIL]

Theoretically whatever expansion device u use, liquid hammering shouldn't happen, because the liquid line should be full with liquid, only if you have a solenoid valve that separates the expansion valve from the liquid , the expansion valve lets the liquid pass and gas is formed before the expansion valve and the solenoid valve, and wen the solenoid valve opens, the liquid hammering happens

fastening of the pipes only reduces the sound effect not the actual hammering that in time damages the components especially the expansion device.

Whatever expansion device is used if the liquid line is full with liquid not hammering can happen (this doesn't exclude vibrations)

[Peter_1]

Devil, if you stop a fast flowing liquid in a fraction of a second, you will get a huge pressure buildup (hydraulic expansion)
This is the case with all EEV ' working with the PWM principle.
Some possibilities to solve: install a T just before the EEV with a piece of copper in the upper part of the T facing up.
Pre-expansion like a member said.
Decrease your HP.
Sure you have 100% liquid at the entrance of the EEV?
Liquid lines not too small (increased velocity)?

[Magoo]

Generally I have found that with pulsing electronic TX valves the hammer is created by high velocity liquid flows before the TX valve, so by increasing the liquid line size or sub-cooling liquid, effectively reducing the liquid velocity you will stop the hammer effect. The hammer will break something sooner than later. Some thing else to look at is the set up on the electronic TX vavs, the response rates are generally controllable, or can be slowed down.

[DEVIL]

Yes peter, i do agree with you, but if the pipe is properly sized and if you don't have a large portion of pipe going straight and then directly going in the EEV without any bends (because elbows reduce the hammering) you can reduce the hammering eave if you can't exclude it all and yes the T facing up, will allow gas to form in the up part and the gas is compressing eliminating the hammering