Luiquid line vibration and liquid hammer

[Infinity]

We have a Bitzer screw compressor Model: HSN7471-75 for R 404 A, with economizer.

And one month ago the liquid line occurs hydraulic hammer, strong vibration, that broke the elbow of the distributor for the evaporator expansion valves.

We shutoff the economizer and the vibrationn and the liquid hammer disappeared.

Analyzing our system and the probable causes, we shutoff the solenoid valve ( being direct pass of the liquid ), but the vibration and liquid hammer still happen.

- Why when we connect the economizer, the liquid line begins the strong vibration and the liquid hammer ?


Does anybody can help me for this problem ?

[NoNickName]

Did they forgot to remove the nozzle from the eco line? There's an application note from Bitzer which explains what differes between liquid injection and economizer. It all ends up in removing a nozzle, should my mind help me.

[Infinity]

Would be possible to let me know the link or if you have that application note from Bitzer ?

You suggest me to remove the nozzle from the eco line ?

[TSK]

When you say economiser do you mean a liquid subcooler because we had this problem before where liquid line components were failing due to fractures, in our case the liquid line was 1-1/8" with a single solenoid valve, when the solenoid valve was de-energised the piston closed against the flow with a resulting hammer action, the problem was resolved by installing a smaller solenoid valve around the main valve, the smaller valve was then de-energised on a delay timer some 15 seconds later. From that moment on the problem was never seen again.

[Infinity]

///TSK: Yes, the economiser is the liquid subcooler.
Our liquid line is 1-1/4" with a single solenoid valve installed close the evaporator. Then you suggest me to install another smaller solenoid valve before the main's one in parallel ?

Please to clarify me about the delay:
The smaller SV de-energized with delay of 15 seconds later after the de-energized of the main SV ?


What is the effect you're reaching for this ?


If the main SV was de-energized, what is the action of this second smaller SV de-energized on a delay of 15 seconds ? Because the piston of the main SV will close anyway against the flow, how will work this second smaller SV de-energezid with delay of 15 seconds ?

And regarding the smaller SV you've installed, how much smaller ?

When you say economiser do you mean a liquid subcooler because we had this problem before where liquid line components were failing due to fractures, in our case the liquid line was 1-1/8" with a single solenoid valve, when the solenoid valve was de-energised the piston closed against the flow with a resulting hammer action, the problem was resolved by installing a smaller solenoid valve around the main valve, the smaller valve was then de-energised on a delay timer some 15 seconds later. From that moment on the problem was never seen again.

[Josip]

Hi, Infinity

Welcome to RE.

We have a Bitzer screw compressor Model: HSN7471-75 for R 404 A, with economizer.

And one month ago the liquid line occurs hydraulic hammer, strong vibration, that broke the elbow of the distributor for the evaporator expansion valves.

We shutoff the economizer and the vibration and the liquid hammer disappeared.

Analyzing our system and the probable causes, we shutoff the solenoid valve ( being direct pass of the liquid ), but the vibration and liquid hammer still happen.

- Why when we connect the economizer, the liquid line begins the strong vibration and the liquid hammer ?


Does anybody can help me for this problem ?

You can also install a motorized valve with very slow motion during opening and closing. Special execution and maybe expensive due to size DN32 (11/4").

Or to install one smaller solenoid by-pass valve as per suggestion...see attached drawing.

If the main SV was de-energized, what is the action of this second smaller SV de-energized on a delay of 15 seconds ? Because the piston of the main SV will close anyway against the flow, how will work this second smaller SV de-energezid with delay of 15 seconds ?

....but you will still have a flow through the small valve for next 15 seconds and you will not have a liquid hammering

You can use revert sequence for opening too. First open small one and then after 15 seconds big one, without more then small tremble.

Small valve can be size of DN10 (3/8") or DN15 (1/2").

Best regards, Josip

[Infinity]

/// Hi JOSIP,
The EV only close and open when they are energized, but our liquid hammer and extremely high liquid line vibration occur while we connect the economizer. Shuttoff the economizer, the liquid hammer and vibration dissapears and the equipment works "normally" but with deficiency in the frozen capacity.
As a proof, we have taken off the the SV, staying connected directly to the expansion valves of the evaportaor. (We close and oppen the liquid line with the hand valve of the receiver tank), but the hydraulic hammer and vibration still there. With this proof we supposed that taking out the SV, there will not have valves that opens or closes, causing the hammering. But still there this problem.

Your proposed solution I think could work if the hidraulic hammer occur while we close the solenoid valve for turn off the compressor. But isn't our case, that vibrates and hammer in full operation of the refrigeration equipment.

Please any comments about it.

Hi, Infinity

Welcome to RE.



You can also install a motorized valve with very slow motion during opening and closing. Special execution and maybe expensive due to size DN32 (11/4").

Or to install one smaller solenoid by-pass valve as per suggestion...see attached drawing.



....but you will still have a flow through the small valve for next 15 seconds and you will not have a liquid hammering

You can use revert sequence for opening too. First open small one and then after 15 seconds big one, without more then small tremble.

Small valve can be size of DN10 (3/8") or DN15 (1/2").

Best regards, Josip

[Infinity]

No way the problem still over there.

Maybe the problem are the evaporator expansion valves....

Because now the liquid flow are directly from the receiver to the evaporator expansion valves without the main solenoid valves. But once we connect the economizer, at few seconds the liquid line begin the hidraulic hammer and huge vibration

Does anybody can help me for this problem ?

[wkd]

Have you tried measuring the compressor intermediate line superheat as most economizers inlet superheated vapor into the compression cycle if this is not superheated it is the same as injecting liquid and will cause liquid hammer and high vibration.Suggest a minimum of 4K superheat.

[TSK]

Sorry there Infinity, I assumed your problem was at solenoid closing, I think you need to check the velocity of refrigerant through the valve, remember that the valve uses the incomming side pressure to close the valve, if PD across valve is too high it could be your problem, rarely can you get a liquid pressure reading after the solenoid valve so you may need to break into the system and fit a 1/4" connection.
If you post the capacity of the plant and the oprerating conditions I am sure Prof Sporlon will pick it up and advise.

[Infinity]

/// Hi TSK, but the way, the SV do not modulate it. So it's difficult to cause hydraulic hammer, because the valve staying open or closed, but never modulate it.
And remeber that now our refrigeration equipment are whitout the solenoid valve. So he stay always open. But still happenning the hidrailic hammer and large vibration.
And remember that our problem begin when we turn on the economizer. And if liquid line start the hammer and large vibration, we just turn off the econoimizer and the problem disappears. And the only difference with the econ on and off, it's the increassing of the flow rate throught the line, I don't know if this data is relevant to solve my problem.

We are discarding the component that could cause the problem, so without the solenoid valve, the problem still over there, thinking about it we have 2 possible hypothesis
1.- The expansion valves are out of range.
2.- The Eco line or the eco, have some problems.


Please to find below the follow data for Prof. Sporlon

compressor: Bitzer HSN 7471-75
Evaporator expansion valve: Danfoss TES 12 # 4 Part nº067B3348
Eco. expansion valve: Danfoss TES 5 # 3 Part nº067B3342
Solenoid valve: Dafoss EVR 20 1 1/8"
sution pipe : 3 1/8"
discharge: 1 1/8"
to rec. : 1 3/8
to solenoid (close to expansion valve): 1 1/8"
from solenoid to expansion valve: 7/8"
Eco Suction : 7/8”

The gas flow rate for the compressor is 250m3/hr,
Eva. tp: -35ºC
Cond. tp: +30ºC
d(t) : 8

Sorry there Infinity, I assumed your problem was at solenoid closing, I think you need to check the velocity of refrigerant through the valve, remember that the valve uses the incomming side pressure to close the valve, if PD across valve is too high it could be your problem, rarely can you get a liquid pressure reading after the solenoid valve so you may need to break into the system and fit a 1/4" connection.
If you post the capacity of the plant and the oprerating conditions I am sure Prof Sporlon will pick it up and advise.

[frank]

If you post the capacity of the plant and the oprerating conditions I am sure Prof Sporlon will pick it up and advise.

The Prof hasn't been on the Forum for over a year now. Methinks he's left us for good.

[tony--1]

Hi Infinity
On R404A gas you should not need to sub cool.