Urgent Issue. Liquid line jumping

[KegSalad]

Hello,

I have an issue on a walk in blast freezer on R449 / 26kg @ -21 setpoint.
The condenser fans cut in at 15 bar and cut out at 18 bar, when the fans cut out at 15 bar the liquid line violently rattles.

I have replaced the expansion valve and checked the solenoid valve, all ok. The pressures are all as per design and it has just had virgin gas charged so it’s not nitrogen etc.

Anyone have an idea or what I could check?

Thanks in advance.

[chemi-cool]

I had something similar once with R22.
There was too much refrigerant in the system.
15 Bar seems too low to me.
Always set one fan working with compressor and keep the head pressure with the other fan.

[KegSalad]

I thought of overcharge too but the pressures would be a lot higher I think.
I think it’s something to do with the fan cycle set up like you say chemi-cool.

Anyone else have any idea’s of things I could try tomorrow?

Thanks

[cricri]

I had similar problem on one R404 plant 10 years ago.
- at first it was low frequency vibrations, liquid hamering. Liquid line (previously for R22) was undersized.
- after replacement we were getting high frequency vibrations. this was coming from the danfoss expansion valve (TEX 5 or 12 dont remember). when expansion valve was closing line started to vibrate. we did some test with each internal parts dissasembled in components from receiver to expansion valve.
clearly it was the expansion valve.
replaced with an electronic one, end of story!

in both situations we faced to pipe breakage and refrigerant losses.

[Glenn Moore]

Most liquid line vibrations, liquid hammer, pulsation ,violent shaking of the liquid line ,leading up often to pipe fractures are mostly caused by 1) heavily sub cooled liquid, 2) expansion orifice size. 3) solenoid valve.

In Kegsalads case the 2 condenser fans are cycled on and off via a single pressure switch. So when the two fans are off the liquid line pressure is rising rapidly, so the expansion valve is being forced to close, to hold the refrigerant back in the liquid line to control the superheat. Once the discharge pressure reaches 18bar the pressure switch switches ON the 2 fans.this causes a rapid pressure fall in the condenser and the liquid line. The liquid is now sucked back towards the condenser as the condenser pressure falls.The expansion valve is now forced to open as its liquid supply has suddenly been badly reduced and the superheat in the cooler starts to rise. At the same time due to the liquid flow in the liquid line rapidly reducing this has an effect on the solenoid ,as the pd (pressure drop) across the solenoid starts to drop the diaphragm starts to close in the valve.
As the discharge pressure falls to the pressure switch cut off point at 15 bar the fans stop and the condenser pressure starts to rise. The liquid line now has flash gas ahead of the liquid being pushed towards the solenoid valve and the expansion valve. As the liquid/flash gas hits the expansion valve orifice this causes shock waves back through the solenoid valve into the liquid line. This liquid is subcooled and full of energy and as it forces its way through the tev orifice the orifice tries to close against this subcooled liquid force. This often causes a reaction between the orifice and the solenoid diaphragm and massive pulsations occur.
This situation destabilises the superheat control of the evaporator as the tev is being forced to open and then close instead of a steady modulation and stable liquid injection. This causes poor cooling efficiency as the evaporator is never fully controlled due to the expansion valve struggling to control .
So I would run one condenser fan continuously with the compressor .This fan must be the one where the liquid exits the condenser . Better still fit a fan speed controller on the 2nd fan to get a fully stable discharge condition . Then adjust the expansion valve to a stable superheat between 5-8k .it may be necessary to change to a smaller orifice and also check that the solenoid diaphragm material is flat and not got a ripple in it as pulsations will stretch the diaphragm material causing an open and close CLICK like opening instead of the easy flip flop action.

In cricri situation this is an old problem with heavy sub cooled liquid using Danfoss TE 12 expansion valves. The TE 12 orifice only has approx 0.9mm stroke from open to close, when the valve is slightly oversized the orifice tries to close against the subcooled liquid . The force of the subcooled liquid tries to force its way past the orifice. The orifce is pushed open and causes the orifice to chatter this causes shock waves back down through the solenoid valve along the liquid line . The liquid line jumps around breaking its brackets and is frightening to watch , on one site I visited an 15/8 liquid line shattered due to this problem. Sometimes by fitting a one size smaller orifice cured the problem as the smaller orifice stayed open to achieve duty and offered little resistance to the liquid flow.
The best solution was to fit an electronic expansion valve as the capacity range and opening of the orifice is far larger than a simple tev ,and the orifice is never causes these problems , seen it ,done it got the Tee shirt

[KegSalad]

Hi Glenn,

What a very detailed reply, I think you have hit the nail on the head with that. The pipe has already fractured several times. It’s also fitted with a Danfoss TE 12 expansion valve as you mentioned.

My plan tomorrow is as you say, knock one of the condenser fans offline and monitor this with just the one fan running and see how it affects running conditions! Thanks very much for your help and I will let you know how it goes.

[Glenn Moore]

The TE 12 is a nightmare for liquid hammer . I was field services manager for Danfoss and the sites that had that problem mainly due to R502 being banned and R22 compound machines with economisers . I was on a plant in Attleborough a chicken slaughter house the liquid line was across the cold room roof .when the pulsations started the liquid line turned into a wriggling snake . I initially jumped on it to stop it wriggling then I just ran before it blew. If the fan control doesn’t work try a one size smaller orifice

[chemi-cool]

Please consider electronic expansion valve.

[KegSalad]

Hi Glenn, So today, I knocked off one of the condenser fans and it didn’t really make any difference. The pipe still rattles around. I removed the expansion valve and checked orifice, number 7 that’s currently in it.

I have ordered a smaller orifice as you recommended and will give this a bash. Are you confident this will be the issue? I very much hope so it I’m lost for ideas... at least it’s Friday.

[Glenn Moore]

Hi Keg do you know the duty of the condensing unit the compressor or evaporator model. If you have any of this info I can doublecheck the Tev selection for you . As I said the problem with the T12 is with its small diaphragm goving only about 0.86mm movement so if never far from it’s closing point which is where the pulsations starts . If you have any system component data send it on and I can check the best solution for you

[KegSalad]

Hi Glenn,

I don’t have that information on me to hand but I will try get back on site over the weekend to note some of the details down and get back to you, really appreciate your help. Thank you.

[mbc]

Hi
Might the solenoid valve is opening partly
If you choose large size for solenoid valve in liquid line then it goes for partly opening condition .
And you have liquid hammer in system

[RANGER1]

Kegsalad,
It would also be interesting what your maximum ambient condition is for this unit design.
It mentions you are from Scotland, is unit in Scotland?

What is ambient now on average.

What if you make fans run continuously and see what happens!

Give details & lengths of system layout would be good as well
liquid receiver to solenoid to expansion valve.

Is there a sight glass? what's it look like in these situations.

If you closed solenoid or stop valve, do things change (experiment a bit).
Thanks

[KegSalad]

Hello,

Yes the ambient air temperature is about 0degrees at the moment. With one fan running only on condenser.

I don’t think I can have one fan running constantly as it’ll take the pressure down to fast. The length of pipe work is only around 5m. Liquid receiver in system, the sight glass looks normal conditions to me when running.

I’m lost with what to do, apart from change orifice size in TXV.

[RANGER1]

Keg salad,
What are your running condition in this 0 deg C ambient.
suction, discharge, subcooling etc
What are cycling times on condenser fan with current pressure set points?

[Glenn Moore]

Hi Keg if your on site this weekend put the adjustment key on the superheat spindle . If the liquid line starts to vibrate turn the spindle anti clockwise to serif the vibration stops then let me know
Glenn

[KegSalad]

Hi Glenn,

I actually tried that today to see if it made any difference, and it still rattled so I put it back to default again.

ranger1 - suction around 1 bar, discharge usually around 16bar, fan cut in 18bar, fan cut out 15 bar. The condenser fan only runs for around 10 seconds.

[RANGER1]

Hi Glenn,

I actually tried that today to see if it made any difference, and it still rattled so I put it back to default again.

ranger1 - suction around 1 bar, discharge usually around 16bar, fan cut in 18bar, fan cut out 15 bar. The condenser fan only runs for around 10 seconds.

So I think 0 deg C ambient set everything down 500 kpa on fan cycling as a starting point.
See what happens.
You could also block some of condenser to reduce it’s capacity to stabilise things.
This will reduce subcooling probably, if Tx valve to big will help derate it.
Check superheat

Currently you have saturated condensing conditions set for 35 deg ambient.

From memory 1500 kpa 38.5 & 1800 kpa 45 deg C saturated
Compressor will run more efficiently, just have to see how to valve reacts.

[KegSalad]

Hi Ranger,

Thanks for your input. I think it is maybe over condensing the fact that it only takes around 10 seconds for 1 out of the 2 fans to switch from 18bar to 15bar. I will try to cover the coil this weekend and do a test run and see how it goes. It it weird though how this is 2 years old and never had any issues until a contractor carried out TXV change and left site again! Hmmmm...

[RANGER1]

Hi Ranger,

Thanks for your input. I think it is maybe over condensing the fact that it only takes around 10 seconds for 1 out of the 2 fans to switch from 18bar to 15bar. I will try to cover the coil this weekend and do a test run and see how it goes. It it weird though how this is 2 years old and never had any issues until a contractor carried out TXV change and left site again! Hmmmm...

Maybe Glenn can sort out Tx valve.
Contractor probably very efficient & old one thrown away.

[mbc]

Hi
What is the pipeing and valves and solenoid valve size in liquid line

Also when fan goes on and off do you have bobble
In the liquid line.?

[KegSalad]

Hi,

Haven’t managed to get to site this weekend due to snow but will be in tomorrow to try these things and to get system details for correct expansion valve type.

Thanks

[KegSalad]

Hi Glenn,

The only details I can find is this-

Evaporator - REFRECO
Model - REBFT 0632 F10E4D
Serial - 2019140300 034

Condenser - ZANOTTI
Model - UNKND75500SA2758
Serial - 1909112A

Not sure if that’s any use?
Cheers

[mbc]

HI

Have a look for partly open at temp.

I just put some information to show you we have partly open in solenoid valves and it open and close with different pressure .

[KegSalad]

I noticed today, I ran it from ambient air temperature @ 8 degrees to -21 degrees.

Switched it on, monitored it and the pipes were not rattling until it gets to temperature and then once it’s hit -19 back up to -21 this is when the liquid hammer starts, don’t know if that makes it more obvious what it could be?

[Glenn Moore]

Hi Keg
I’ll see what I can find on these units , but the compressor model would be helpful
From everything you’ve said about the operation of this unit it certainly sounds that the condenser fans or at least 1 fan could do with a fan speed controller on it to stabilise the discharge pressure but the liquid sub cooling is making the Tev orifice oversized for the duty of the unit . By fitting a smaller orifice the orifice opening should prevent liquid hammer taking place.
Fitting an electronic expansion valve is the final solution if fitting the smaller orifice fails.
But I would consider also fitting a fan speed controller as the rapid rise and fall over a 10 second cycle will have an effect on the compressor winding with the surge in current which has the potential to take the windings out . I’ll come back tomorrow when I have a chance to find out what duty that unit can do Glenn

[mbc]

Hi
I had same issues in CSH 8553 Bitzer 110hp
It was 4 step with 4 solenoid valve 5/8
Castel .
Air Cold Condenser is working with 3 high pressure controls.
About 8 years ago After I started
I saw some times it happening
Frist I thought something wrong in our wiring but it was ok .
Then I took inside of solenoid valve
It did not happen again
In one month I closed 1/2 inlet valve before solenoid valve .
Then I changed solenoid valve to 1/2

[alexaben]

why remove my comment

[Brian_UK]

why remove my comment
Because it only contained poorly copied text from other posts and made no intelligent sense.