New member

[Dorf]

Hello everybody,
I am a new member to your community (from Greece) and I wish everybody health and good luck.
I am a Dipl. Mechanical & Electrical Engineer, dealing with Refrigeration and Air Conditioning Plants.

By the way, does anybody have any idea about how to face the serious "liquid hammer" in liquid lines when
R.404A is used ?
I think that a good idea would be to use two (2) separate Solenoid Valves : the main (and proper) one, as well as another (small) one that will open first to "break" the pressure and after two or three secs the main one will be opened. The 'closing' will take place in the opposite way.
Do you think it is a good idea ?
Does anybody have some relevant experience or any other idea ?

Dorf

[US Iceman]

Hi Dorf,

Welcome to the Re forums.

For your first question, you picked a good one!;)

Liquid hammer occurs when the liquid velocity is too high and a quick-closing valve actuates closed. For each refrigerant it is slightly different because each refrigerant has it's own acoustic velocity (or speed of sound).

You cannot regulate the valve closing speed as the solenoid valves are relatively "quick-opening". Therefore, the best method is to slow down the liquid by using a larger line.

In water plumbing systems they use a pulsation dampener to absorb the shock wave that is created by the valve closing. Something like this could work for refrigerant is you could guarantee a gas cushion on top of the liquid in the dampener device. The gas volume acts as a shock absorber, instead of the piping, fittings, and valves.

[Dorf]

Many thanks Iceman, for your respond.
It looks apparent to slow down the liquid by using a larger line (though the cost for an extended plant as the one I have in mind - 3.000 m2 - will be big enough), but how much larger could it be ?
Is it a good idea to use just the 'next' standard diameter of the calculated one ?
Anyway, experimentally I found out that my proposed 'method' of two separate Solenoid valves per Evaporator, is a significant (and far cheeper) relief of the problem.
I agree that the apparent solution of larger Liquid lines offers a more 'distribution balanced' system (especially for a big plant), but the added cost is a serious problem.

Dorf

[lana]

Hi Drof and welcome to the RE.

In EN378 standard is mentioned that the liquid hammer can be minimized if the solenoid valve is placed as near as possible to the TEV, i.e. inside the cold room and just before the TEV.

I attach a page from the standard, I hope this helps.
Cheers

[US Iceman]

Dorf,

Your use of two solenoid valves was mentioned in the attachment lana supplied. A pilot solenoid used to slow down the instantaneous shock is one method that can be used.

This scheme is recommended on hot gas defrost systems where large evaporator coils are used also. Although this is based on vapor propelled liquid more than the simpler liquid hammer.

The damage generated from the sudden valve closure is based on how fast the liquid is moving in the liquid line. When the valve closes the energy of the high velocity liquid is transferred into a shock wave. This wave reflects through the piping until the energy is dissipated.

The mention of placing the solenoid close to the TXV would seem to indicate you would have more piping and perhaps more elbows upstream of the solenoid valve. This could provide more flexibility in the piping that could absorb some of this energy and prevent a line rupture of fitting failure.

I realize the larger pipe is more expensive, but in my mind I prefer to treat the cause of the problem.

[Dorf]

Thanks Lana and Iceman.
Your notes are helpful and wellcomed.

Dorf