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Samarjit Sen
17-03-2008, 08:13 AM
Could some one please let me know the reason for the frequent breakage of the discharge valve reed of a reciprocating refrigeration compressor. The compressor is operating at -35 oC Te and 40 oC Tc.

Thanks in advance

NoNickName
17-03-2008, 08:45 AM
Liquid hit

dogma
17-03-2008, 08:48 AM
many reasons. Liquid getting back to compressor?

Peter_1
17-03-2008, 08:59 AM
Other possible cause, to high superheat resulting in a very high discharge temperature?

Samarjit Sen
17-03-2008, 09:31 AM
If we reduce the superheat, then there would be a flood back of liquid. I just now accross an article a part of which I am stating as hereunder.
"In positive displacement compressors such as reciprocating refrigerant compressors, gaseous refrigerant is drawn into a cylinder and is then compressed due to the movement of the piston in the bore. The piston acts against the trapped volume causing it to decrease in volume and increase in pressure. When the pressure increases to a point sufficient to overcome the bias of the discharge (http://www.patentstorm.us/patents/5706850-description.html) valve together with the discharge pressure acting on the discharge side of the valve, the valve is opened and the compressed gas is discharged from the cylinder. This process can be repeated hundreds of times each minute of operation. Problems arise, particularly at start up when more than the normal nominal amounts of oil, an incompressible material, are fed to the cylinder. The problems result from the dense oil impinging upon the reed(s) of the suction valve(s) due to inertial forces and from the volume that has to be discharged in the small time available. The oil flowing into the cylinder with the rapidly flowing gas does not flow around the reed because of inertial forces and, in impinging upon the reed, tends to cause it to be driven against its valve stop which can damage the reed"

They advice in installing an Oil Diffuser. What is an Oil Diffuser and do you agree to the above. Will it solve my problem.

Samarjit Sen
17-03-2008, 10:15 AM
In case there is a liquid returning to the compressor, then as far as I now that the suction reeds would be damaged. In this case it is the discharge reeds. Please correct me if I am wrong.

Samarjit Sen
17-03-2008, 10:27 AM
Hello Nike 123,

I am using Dorin semi hermetic compressor model K 2500 CB.

I shall go through the book provided by you and shall revert back to you.

nike123
17-03-2008, 10:28 AM
I think, if liquid enters the cylinder then it will broke discharge reed because liquid could not be compressed and mechanical force of shaft is directly exerted to discharge reed.

Some compressor manufactures (Copeland) have spring that allows some dislocation of valve and small amount of liquid to pass without breaking of discharge valve.

I have description somewhere, but I need to find it.

What compressor you are talking about?

Here you have book with lots of details about valves and causes of failure:
http://www.refrigeration-engineer.com/forums/showthread.php?t=11202&highlight=book

I think you already have it! Page 157.

monkey spanners
17-03-2008, 11:50 AM
Found this on the CMP site

http://www.cmpcorp.com/files/techman.pdf

Has a little bit at the start about compressor failure, one thing it states is that high discharge temperatures will discolour the valve plate and the discolouring will not rub off.

I once turned some reed valves over due to a wear ring on them to get a compressor pumping again, they lasted about a week or so before breaking. I put this down to them now being bent in the opposite direction. Are they being put back in the same way they were?

I once saw the suction valve retaining pin of a copeland compressor fired through the valve plate, leaving only a shiny mark on the cylinderhead. Its amazing what hydraulic pressure can develope in compressors pumping liquid.
Are the discharge valve retaining plates/fingers ok and not bent up more than they should be and thus allowing more flex in the valve reeds than normal?

Jon

Samarjit Sen
17-03-2008, 12:17 PM
Hello Jon,

Thank you for your help. I feel that due to high discharge temperature this is happenng. Although DTC are provided in the compressor.

Can you suggest as to how can it be rectified and what measures should be taken.

nike123
17-03-2008, 12:39 PM
Hello Nike 123,

I am using Dorin semi hermetic compressor model K 2500 CB.

I shall go through the book provided by you and shall revert back to you.

What is the refrigerant and how you cool head of compressor? What is subcooling, evaporator and total superheat if you know these values.

Also, read this:
http://www.dorin.com/documents/Download/attach/BT_004-07A.pdf

Samarjit Sen
17-03-2008, 01:14 PM
Thank you nike 123,

We have the documents of the Dorin. We are operating the compressor at -35 oC Te and 40 oC Tc with R 22. Regarding the rest of the informations I have asked my people there at site to have it sent to me. The compressors are with DTC. Initially when we commissioned the plant a temperature of -38 oC was being maintained inside the Room. Now after a year problems like broken reeds ( discharge) has come up. We have conveyed these to Dorin.

I feel that there is a problem with the DTC which is not performing as it should. Or as you said earlier liquid is coming to the compressor.

However I really appreciate the care and attention provided by the RE members as not only it is giving me the strength to work it out, but the suggestions and the documents being provided is helping me to short list the defects.

nike123
17-03-2008, 01:27 PM
Do you have head cooling fan or water cooling head? Or you don't have any cooling head option?

US Iceman
17-03-2008, 01:56 PM
Hi Samarjit,



The compressors are with DTC. ..... Now after a year problems like broken reeds ( discharge) has come up.


I am assuming DTC represents "Discharge Temperature Control". How is this accomplished on the compressor?

Are the discharge valve reeds discolored and broken or only broken? As mentioned earlier high temperatures will cause the metal to turn colors.

However, if the reeds are breaking after one year and you have some form of "liquid injection (DTC) into the compressor for temperature control" the broken reeds are probably caused by repeated small liquid slugs.

You did not mention anything about discharge temperature or discharge superheat. These will tell you quite quickly if the problem is temperature related or not.

Samarjit Sen
17-03-2008, 02:04 PM
nike 123.

There are no head cooling fan nor water jackets. But now I think I shall provide at least a head fan on each compressor head along with the DTC ( Discharge temperature Controller )

Samarjit Sen
17-03-2008, 02:09 PM
Mike,

The DTC id Discharge temperature controller as correctly presumed by you. It is a an expansion valve which operates when the sensor senses a high temperature in the head. It is directly fitted on the head and injects vapour into the head.

The colour of the reeds have not changed. It has just broken. I now feel it is due to the small quantity of liquid over these period.

US Iceman
17-03-2008, 02:16 PM
It is directly fitted on the head and injects vapour into the head.


vapor injection??? How is that supposed to cool anything? If the DTC valve has a liquid line feeding it and the outlet of the valve is connected to the compressor, the outlet from the DTC valve will have a small volume of liquid in it in aerosol form.

I forgot to mention the oil diffuser.... this seems like a way to sell a product. I would not use one of these.

nike123
17-03-2008, 02:27 PM
Head cooling fan and DTC together are mandatory for that application, (-35°C evaporation and 40°C condensation with R22) when you have total superheat higher then 20K.
In Fact Head cooling option is mandatory and DTC is only helping.

Your field of aplication is E:
http://farm3.static.flickr.com/2116/2339946563_0db0b652f9_o_d.jpg

Said that, your decision to fit head cooling fans is the right one.
You should also consider water cooled head as better solution if it is plausible to local conditions.

nike123
17-03-2008, 02:30 PM
vapor injection??? How is that supposed to cool anything? If the DTC valve has a liquid line feeding it and the outlet of the valve is connected to the compressor, the outlet from the DTC valve will have a small volume of liquid in it in aerosol form.

I forgot to mention the oil diffuser.... this seems like a way to sell a product. I would not use one of these.

Please, read that document which is in my reply to Samarjit Sen!

This is link!
http://www.dorin.com/documents/Downl...BT_004-07A.pdf (http://www.dorin.com/documents/Download/attach/BT_004-07A.pdf)

Samarjit Sen
17-03-2008, 02:56 PM
Hi Mike,

You are absolutely correct. The DTC has a line feeding it from the liquid line, and the outlet is connected through a distributor to the 3 heads. A small amount of liquid is being injected which keeps the head cool. I do not how effective it is, but so far it has been working.

I have a feeling that the the DTC is not bieng so effective now. However I have asked my people there to change the reeds and also to clean the DTC pipe lines. I am arranging to get the sensors replaced as it may be possible that they may not be working. Further I am going to install head fans.

Samarjit Sen
17-03-2008, 03:01 PM
Hello nike 123,

It is not possible to have a water jacket at this stage now. However a fan can be provided on each compressor. However I feel that the compressor manufacturers should state the facts and provide the requisite support. I had very clearly stated my requirement and had enquired about the additional cooling with fan, which they said is not required. It is my mistake that I did not go deep into this at that stage.

nike123
17-03-2008, 03:20 PM
Hello nike 123,

It is not possible to have a water jacket at this stage now.

Do you mean water cooled head instead of jacket? I don't know of any "jacket" by Dorin.

Samarjit Sen
17-03-2008, 03:43 PM
I meant water cooled head. Sorry nike.

US Iceman
17-03-2008, 03:52 PM
The regulation of the discharge temperature is realised by injecting a “liquid fog”, taken from the liquid receiver, in the suction room, immediately after the electrical motor and before the cylinders.


Evaporation of the thin droplet cools the suction gas which allows to maintain the discharge temperature inferior at the limit value. The quantity of liquid injected is continuously controlled by a microprocessor which in conjunction with a sensor (situated on the discharge manifold) regulates the gas temperature and cycles with a rapid pulse a solenoid valves positioned prior the injector.


Which states exactly what I thought. This is not vapor injection. It's liquid injection. It is basically a TXV used to desuperheat the suction vapor before it is compressed. If this valve or the controller is off just a little then you could overfeed the compressor and break valves.

SteinarN
17-03-2008, 03:55 PM
I have also experienced valve plate failures with that Dorin compressor. It was however a suction valve failure.

Exactly where is the DTC liquid injected in the compressor? Does the compressor run at high evaporation after defrost? Have you measured the disharge gas temperature?
Have you noticed a restrictor plate between the compressor head and the discharge valve? Try to remove this restrictor plate.
If the compressor stops, is the DTC disabled completely then?

nike123
17-03-2008, 04:09 PM
It is basically EEV, and yes, if it is malfunctioning it could damage valve. That is why is important to have head cooling. If head is cooled good then this valve doesn't operate at all.

nike123
17-03-2008, 04:16 PM
I have also experienced valve plate failures with that Dorin compressor. It was however a suction valve failure.

Exactly where is the DTC liquid injected in the compressor?

Immediately after the electrical motor and before the cylinders.


If the compressor stops, is the DTC disabled completely then?
It is also recommended to fit a
solenoid valve which, supplied in
parallel with the contactor of the
compressor, close the liquid line
of the DTC when the compressor
is stopped. In order to avoid risk
of liquid migration inside the
crankcase of the compressor
trough the injection solenoid
valve.

Which reminds me to ask Samarjit Sen did he installed that solenoid valve.

nike123
17-03-2008, 04:23 PM
I meant water cooled head. Sorry nike.
Do you have installed solenoid valve in liquid line of DTC connected to compressor contactor?

US Iceman
17-03-2008, 04:36 PM
Do you have installed solenoid valve in liquid line of DTC connected to compressor contactor?

If not, then that could be big problem!:(

powell
17-03-2008, 05:09 PM
Mike,
The colour of the reeds have not changed. It has just broken. I now feel it is due to the small quantity of liquid over these period.

I believe your on the correct path now.;)

Samarjit Sen
17-03-2008, 05:27 PM
Mike and nike,

No there is no solenoid valve on the luid line entering the DTC. The DTc is connected to a microprocessor unit. I was made to understand that the DTC is actuated/activated by the miceoprocessor on sensing the temperature of the head. There is a sensor attached to the head which is connected to the microprocessor unit.

I was also proposing to install a solenoid valve at the liquid inlet to the DTC, but was told that it is not required.

Maybe what Mike is saying is the actual fact. However I shall have to look into the manuals once again

nike123
17-03-2008, 05:38 PM
In manual, it is solenoid valve in schematic diagram (no. 9) and it is described in text, as you see from my quote.
http://farm4.static.flickr.com/3093/2341213292_cb7acdb202_o_d.jpg

http://farm3.static.flickr.com/2026/2340380289_cfe9a1b936_o_d.jpg

Samarjit Sen
17-03-2008, 05:41 PM
Mike,

The DTC is with the solenoid valve. The complete layout is stated in the link which nike has provided. Further I shall download the bulletin on DTC which was sent by Dorin. The installation has been done as per the direction stated therein.

US Iceman
17-03-2008, 05:46 PM
Someone could have told you the solenoid valve was not required because they thought it might provide shut-off to the liquid flow. I think some off the electronic modulating valves offer that kind of capability however, I would feel a lot more comfortable knowing I had a solenoid valve to provide a positive shut-off.

The solenoid should be wired in parallel with the motor contactor/starter to ensure the solenoid is off when the compressor is off.

Samarjit Sen
17-03-2008, 05:55 PM
Mike,

Here is the link to the DTC Bulletin.

http://download.yousendit.com/4ABC52866E725E69 (http://download.yousendit.com/4ABC52866E725E69)

The pipe line,the wiring etc. has been done as per the instruction. The solenoid valve is an inbuilt attachment to the DTC.

Now I feel that the sensors are not operating due to which this problem has come up. I have asked to have the sensors changed and a fan put over the head as an additional cooling for each compressor.

nike123
17-03-2008, 05:58 PM
Mike,

The DTC is with the solenoid valve. The complete layout is stated in the link which nike has provided. Further I shall download the bulletin on DTC which was sent by Dorin. The installation has been done as per the direction stated therein.


If you are referring at no.3 at diagram, that is modulating solenoid of DTC, and not solenoid valve.
If you are referring at no.9, and it is present on that your particular case, than you have correct instalation.

monkey spanners
17-03-2008, 06:01 PM
If you have a solenoid valve (interlocked with the compressor contactor) before the DTC valve and the DTC valve provides a positive shut off , then would i be correct in thinking that you would need a check valve parallel with the solenoid but flowing backwards to allow any pressure buildup in the line between the solenoid valve and DTC to bleed back to the liquid line in the off cycle should the temperature increase?

I guess not as one isn't shown in the link by Nike.

Jon

Samarjit Sen
18-03-2008, 01:43 AM
Thank you all dear freinds for the information and advices given. I think now I realise the mistakes made by us. I shall be putting a Solenoid valve in the line to the DTC just before it and connect the same to the Compressor contactor, so that when the compressor starts this will be activated . In addition to this I shall be putting fans over each head of the compressor.

I am sure with these changes, my problem should be over.

US Iceman
18-03-2008, 02:26 AM
Samarjit,

Please make sure you insulate the temperature measuring instrument so that the airflow of the fan does not affect the DTC valve operation. A small detail...