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bernard
06-12-2005, 09:23 PM
Hi

Recently had carlye compressor fail.Found the suction hotter than the discharge.Removed the heads and found 3 of the 4 reeds broken.

Would I be correct in saying that this would not cause discharge to pass over into the suction.This would only happen if the internal check valve was passing.

Pack was suffering from flood back.

Regards Bernard

US Iceman
06-12-2005, 11:43 PM
The problem sounds like broken discharge valves. However, internal relief valves act the same way.

When the discharge valves are broken, the gas is compressed, but re-expands into the cylinder when the piston moves back down. The discharge valve could be thought of as a check valve. If the valve is broken, the gas flow is reversed during the suction stroke. When the same gas is compressed again, it gets much hotter.

Internal relief valves do the same thing. The hot discharge gas is bypassed through the internal relief valve back to suction.

If you had liquid get into the compressor, the valves broke during compression (or attempting to compress the liquid).

This is fairly common on flood-back problems.

chiller563
07-12-2005, 12:22 AM
In all probability you have broken suction reeds? This would cause partially compressed superheated vapor to be pushed into the suction area. Most instances of liquid flooding cause suction reeds to break, not discharge. The discharge reed still opens on the compression stroke and liquid is "sprayed" out. However, the suction reed, being closed on the compression stroke, fails due to the excessive high pressures in the cylinder from the liquid attemptiong to be compressed. There are times when a discharge reed will fail under these conditions, but not commonly. If the discharge is broken it usually is caused by a piece of the suction reed or piston that was broken off and tried to get through the port.

Chill

US Iceman
07-12-2005, 02:14 AM
I disagree. It is in all likelihood the discharge valves that have broken.


The discharge reed still opens on the compression stroke and liquid is "sprayed" out.

The liquid does not spray out. Well... some might, but, the pressure is generated so quickly (and very high) the discharge reed backing plates bend and the discharge reeds snap off.

The cylinder with the broken discharge valve does not cool (no suction mass flow) and the cylinder heats up.

You can usually tell which cylinder has been affected by feeling the suction side of the compressor head. If one cylinder is noticeably warmer than the others, it is probably the one with the broken discharge valve.

Another way to check this is to measure the discharge gas temperature. It will be higher than normal due to the re-compression of vapor.

Broken discharge valves are almost always caused by liquid slugging (oil or refrigerant).

The internal relief may have opened during all of this also. If the compressor appears to be OK, replace the valve plate and start it up. If the discharge temperatures are still to high, the internal relief valve may have not re-seated properly.

See the attachment from Copeland's Refrigeration Manual, Part 5.

I'm sticking with my orginal answer...