Liquid Line's Vibration

[JERRYCOOL]

could anybody tell me anything about the liquid lines vibration? the system is a simple system. it's equiped with a copeland compressor(192m3/hr),a shell-tube economizer, a hp-rec., a DX-evap., a surge drum. The liquid line will start amazing vibration after the solenoid valve of the liquid line energized. The liquid is subcooled to 0C and the line is insulated so it seems to me that the flash gas will not happen to this line.

best regards
Jerrycool

[Peter_1]

Almost for sure a too big SV installed, especially when you have liquid subcool and long liquid lines, sometimes with a too small diameter.
It is probably a fast repeating knocking noise and the SV is far away from the receiver.
Give us some figures of capacity, length of the lines, size of the SV and the lines, Tc, Tv, SC.

The too big SV opens so wide and this sudden large amount of velocity increase drops the pressure in the line so fast whereby there isn't sufficient pressure remaining in the liquid line to let the valve stay open.
The valve closes due to this sudden very fast pressure drop but due to the closing of the valve, pressure builds up again and the valve opens again. This phenomena is repeating constantly with very big and dangerous pulsations along the lines.
We once had troubles with this on some cabinets - those furthest away from the receiver - in a supermarket with a pack.

You have to check the KV value for the SV in this case.
Marc O' Brien wrote - as far as I can remeber - a good article about this on his website.
Hey Marc... are you still living or laying on your back somewhere under the sun? .

[chillyhamster]

Dont quite follow your answer Peter, When the solenoid valve is energised, the pressure drop assists the magnetic effect to open the valve. If the coil is continually energised it will not close under any change in pressure, once the coil is de-energised the spring and liquid pressure will close the valve. I therfor cannot see the SV causing the problem.. What type of expansion device is fitted to the system. A Danfoss AKV is well known for causing vibration and harmonics in pipework.

[Peter_1]

Depends if the SV is a direct acting or a servo operated.
BESC5240 can tell us also more about this phenomena I suppose. I think we discussed this once together after we encountered these problems in a supermarket.

[JERRYCOOL]

the solenoid valve on the liquid line is direct action and the expansion valve is Danfoss TEX.
we shutoff the DX-Economizer's expansion valve line, now there is no vibration. But I don't know the reason for it. The Economizer is Plate-exchanger.

[Victorman]

Hi jerrycool
According to The Plumbers Handbook, hydraulic shock occurs when fluid flowing through a pipe is subjected to a sudden , rapid change in velocity , the pressure wave generated travels back and forth within the pipe until the energy is dissipated.
This happens in small diameter pipes , and a quick opening and closing of a valve.
I wonder if a slow acting solenoid is necessary.

P.S. A schematic of the system is in the order of magnitud.

[dill]

Iv'e experienced this before in a similar system to the one you are having the trouble with. It was eventually discovered that the liquid line was incorrectly sized. As well as vibrating it also hummed a strange tune which I thought was hillerious but the customer was'nt too pleased. The line was replaced after the project guy did his callcs again.

[paulcollis]

hi all, tell me, once the liquid line valve has opened for a few seconds does the noise stop ? if it does it sound to me like you are experiencing liquid hammer, if the solenoid valve is situated at the compressor set, and the evaporator is a fair distance away, when the system is pumped down and sitting at say 10 PSI and the valve opens, liquid fills the empty pipe at 200 PSI (depending on refrigerant of course), this inruss of liquid can inturn cause a loud bang and in some cases, i have seen sites we have taken over, were the liquid lines have broken there brackets with the force of liquid hammer, we always install our sol valves as close to the evaporators as possible, not only does this stop hammer but it cuts down the amount of capacity required in your receiver for pump down.

[JERRYCOOL]

1 months ago, we met the same problem in another system(a similar system). The elbow of the liquid line was broken by the vibration. I turn off the Econ., the vibration stopped, but the capacity was not enough. We didn't meet the problem during the first operation of the equipment. The vibration occured after we changed some parts of it. So we doubted that the vibration was caused by noncondensable air inside the system. After reevacuating the system, the problem disappeared. it seems that the problem was solved. But now, the problem happened again. Maybe some ghost cause the problem!!! so mysterious.

[BESC5240]

... If the coil is continually energised it will not close under any change in pressure,....

I do not quiet agree. When the coil on a normally open servo-operated solenoid valve is energized, the valve will close when there isn't a minimum pressure drop over the valve. It's this pressure difference that presses the diagram away from the main orifice of the valve and opens it for full flow. You need this pressure drop to open the valve and to keep it open.

Jerrycool,
It seems to me the solenoid valve is oversized when using subcooled liquid. Could you tell which refrigerant you use and what the type (and brand) of solenoid valve is?

[US Iceman]

Hydraulic hammer occurs when the velocity in the line is suddenly stopped as Victorman said before. Part of what determines if the valve is a quick-opening valve is dependent on the upstream length of the pipe and the acoustic velocity of the refrigerant in whatever state (liquid or vapor) the refrigerant is in.

The acoustic velocity is the same as the speed of sound for the refrigerant. This is slightly different for vapor or liquid and depends on the actual density.

If the valve itself closes faster than the time it takes for the pressure wave to travel from the valve, back to the opposite end of the pipe and back to the valve, the valve opening can be classified as quick opening. This is where you get the sudden dramatic increase in pressure.

If the valve closes slower than this, hydraulic shock should not be the problem.

I have seen a similar problem to the line "vibration" on oil injection lines in screw compressors. Part of the problem was due to the rotor tips spinning past the oil injection port. Another part of the problem was due to the piping. I do not remember all of the details for the correction, just that this was a very strange problem to solve. This was someone elses project, so I only heard some of the details.

My best guess without any additional details is that the liquid line solenoid is pulsating at the same frequency as the compressor rotor tip frequency, or something similar to this.

The vibration occurred after we changed some parts of it.

What parts were changed??? What ever was changed has a contributing effect to the problem.

[JERRYCOOL]

We doubt this before and installed a small bypass solenoid valve for the main solenoid valve to slow the shock. But vibration is still there. Or do you have any better solution?

The part we changed is an elbow at liquid line. This system's vibration happened after we changed the elbow. But for another system, the vibration exists since commission. We have same system in taiwan without vibration. But the only difference as taiwan guys said is the location of evaporator. Their evaporator locates below the condensing unit. But i don't think it will affect anything, since the liquid is subcooled.

followed is the components we used for the system, and some technical details for the system. maybe it will be help for troubleshooting:
compressor: Bitzer HSN 7451-60
expansion valve: Danfoss TEX 12-18 7/8"
solenoid valve: Dafoss EVR 20 1 1/8"
sution pipe : 3 1/8"
discharge: 1 5/8"
to rec. : 1 3/8
to solenoid (close to expansion valve): 1 1/8"
from solenoid to expansion valve: 7/8"

The gas flow rate for the compressor is 192m3/hr,
Eva. tp: -40C
Cond. tp: 45C
Lp flow rate: 661kg/hr
hp flow rate: 937kg/hr
Econ flow rate: 276kg/hr

[Peter_1]

Waw, what a nice drawing of a perfect set-up on the first sight.
Which valve exactly did you bypassed?

[BESC5240]

Hi Jerrycool,
You did not mention the refrigerant, but as the expansion valve is a TEX, I presume it's R22.
I have entered your data in the Bitzer software (version 4.1) and have then used the Danfoss Dircalc software to check the size of the solenoid valve.
As you can see in the attachment EVR20.pdf , the EVR20 is far too big for this unit. The pressure drop over this valve is only 0,0139 bar. The minimum pressure drop to open this valve (and to keep it open) is 0,05 bar.
You should use a EVR15 (see other attachment). Here the pressure drop is 0,0515 (which is above the minimum). Altough the EVR15 has only a connection of 7/8" this is the valve you should use.

[US Iceman]

we shutoff the DX-Economizer's expansion valve line, now there is no vibration.

If closing the liquid line to the economizer can stop the vibration, this would seem to indicate the mass flow increased through the main liquid line. The increase in mass flow through the main liquid line may create sufficient pressure drop to keep the main liquid line solenoid valve open.

After re-evacuating the system, the problem disappeared. it seems that the problem was solved. But now, the problem happened again.

Here again this appears to provide some information. After evacuating the system, the system would experience a higher load to pull the temperatures back down. During this time, the mass flow through the system would be higher. Therefore, the higher mass flow could keep the main solenoid valve open.

From my past experience I think Peter_1 and BESC5240 are on the right path. Control valves (solenoids and regulators) should never be sized by pipe diameter. The valve flow coefficient (Kv) should always be used to select the correct valve port.

Pilot operated (or servo-operated) valves can present some problems since they depend on the pressure difference to keep them open.

The part we changed is an elbow at liquid line. This system's vibration happened after we changed the elbow. But for another system, the vibration exists since commission.

If the vibration started after the elbow was changed, why was the elbow changed in the first place? Was it cracked from earlier vibration?

We have same system in Taiwan without vibration. But the only difference as Taiwan guys said is the location of evaporator.

There are always differences even if the same equipment is used. Installation of equipment, valves, piping, or how fittings are used can be subtle differences that are sometimes missed.

[JERRYCOOL]

HI, Usiceman
i checked the danfoss catalog. it says that the EVR20's capacity is 101kw with 0.15bar pressure drop based on -10C ET and 25C CT. My system's capacity is only about 30-40kw. So the solenoid valve is obiviously big. But i don't know if it's big enough to cause the problem. The danfoss people can't tell me this. they don't know the actual pressure drop across the valve. The valve needs at least 0.05bar pressure difference to keep the valve open.
Could you tell me how to caculate the pressure drop? The Kv value is 5m3/h.(it says" the kv value is the water flow in m3/h at a pressure drop across valve of 1 bar, density 1000kg/m3.)
Thanks

[Peter_1]

Jerrycool,

If you don't mount a smaller valve, then that's your choice. But the one installed now is far too big, as stated already in my first post.

You still didn't answer my question: what valve did you bypassed and what size have you installed?
What are the valve opening sequences?

BESC5240 remembers probably the sequence we followed at the poultry slaughtery when hotgas defrosting the blast freezer.
The whole setup was a complete nightmare.

It's up to you if you want to solve your problem. Eliminate all possible causes and the SV is one possible cause because it's according to the Danfoss specs completely out of range.

I know BESC5240, and if there's one person you have to believe or trust because of this specific knowledge, it's him.

There is also the condensing pressure and what's also is very important is the distance between receiver and SV, the longer the more change this will happen.
By the way, how long is the line between reciever and Sv and is there a height difference?

What DP pressure you have on a long line you think the moment the valve fully opens? There's then a huge drop of 'supplying pressure'

[BESC5240]

.... the solenoid valve is obiviously big. But i don't know if it's big enough to cause the problem.

A too big solenoid valve can cause serious problems. I have seen excessive wear out on TEV and liquid lines broken due to this. Replacing the SV's solved the problem.

.... The danfoss people can't tell me this. they don't know the actual pressure drop across the valve. The valve needs at least 0.05bar pressure difference to keep the valve open.
Could you tell me how to caculate the pressure drop?

This means you are not talking to the right person at Danfoss (China?).
If you look at the attachments I sent earlier you will see I have calculated the pressure drops for you with a software DIRCALC. You can download this software for free on every Danfoss site.

[cruzeiros]

You can download this software for free on every Danfoss site.

however..can you post the link please.

[BESC5240]

however..can you post the link please.

Hi Cruzeiros,
I can see I was too quick on writing 'every danfoss site'. It's not directly available on the site in Romania (www.danfoss.ro). But I'm sure if you contact Danfoss in Bucuresti (danfoss.ro@danfoss.com) they can send you the program.

If not this is the link for the UK:

http://www.danfoss.com/United_Kingdo...tion+Tools.htm

I'm from Belgium. Here the link is :
http://be.refrignet.danfoss.com/SW/BERA_Registration/nl_be/index.htm?click=i_{E3D48AE3-D20F-4006-B769-AAD8DA429E73}


(You'll have to register first)

[JERRYCOOL]

i was going to make some modificaiton to the system weeks before. But it is unbelieveable that when i started the system again, the vibration disappeared. We tried to start the unit again and again, and hope to see the problems again, but we failed. We did nothing to the system.
And we tried to raise the condensing presssure, but the problem still didn't happen. So it makes no sense to say that it is because the cold weather. about 0C.
We are going to test the unit again in hot days, I expect to find something new and interesting.
Does anybody have some good ideas about it?