Too Hot!

[SIGNSTU]

I have 2 sabroe smc 106 6 cly comp.,one runs a discharge temp. of 300deg (F) the other is 240.They both go to a common line to the cooling tower and both have the same load. We are running ammona 717 with a flooded chiller. It is water cooled and the flow is good,and the water jackets are clean.I removed the 1 head that is loaded all the time to check the valves and with no surprise they were like brand new. I understand there is a bypass valve that could leak but the block temp. at the valve is the same, any ideas?

[US Iceman]

If the discharge valves (all of them) are in good condition, and the internal relief valve is not leaking, then the high temperatures you are seeing may just be the result of the compressors running partially unloaded for long periods.

You mentioned this was a flooded (water?) chiller, so you should not have a problem with high suction superheat (if the liquid level is OK in the chiller).

Is the compressor running at 240F operating with more cylinders loaded, than the compressor running at 300F?

[Josip]

Hi, SIGNSTU :)


I have 2 sabroe smc 106 6 cly comp.,one runs a discharge temp. of 300deg (F) the other is 240.They both go to a common line to the cooling tower and both have the same load. We are running ammona 717 with a flooded chiller. It is water cooled and the flow is good,and the water jackets are clean.I removed the 1 head that is loaded all the time to check the valves and with no surprise they were like brand new. I understand there is a bypass valve that could leak but the block temp. at the valve is the same, any ideas?

Is it possible that the "hot" compressor is connected to suction pipe after the "cold" one;)

Maybe you can unload the first "cold" one to 66%-4 cyl and load the second "hot" one to 100% and then check discharge temp.

Do you have UNISAB II installed with your compressors. Check suction superheat.


Anyhow please check attached fault list with some codes.

Best regards, Josip :)

[SIGNSTU]

This is a flooded chiller that has 2 suction lines that come off the top of the chiller so the super heat should be the same. As far as codes, it just shows the discharge temp is 50-80 deg. (f) hotter than the other. I think it is the internial bypass valve but all test show no.i did not want to spend $1300 for a new valve if it was not needed but its coming.

[US Iceman]

If the internal relief valve is leaking I think the discharge temperature would be a lot higher, unless it is just leaking a small amount. If that is the case, you need to find out what caused the valve to lift in the first place.

If it has lifted, you must have experienced a high pressure condition such as; high discharge pressure in the system, or someone started the compressor with the discharge service valve closed.

In my experience it's not uncommon to see the discharge temperature increase at low loads. During these conditions the compressor has a lower mass flow. This tends to increase the discharge temperature.

As the compressor loads up, the mass flow increases and the discharge temperature starts to return to normal levels.

Without any answers to the questions posted, it's hard to say what the actual cause is.

[NH3LVR]

Welcome to the Forum Signstu:)

I have no experience with Sabroe Piston Machines, but can tell you how I would approach this with a Mycom or Vilter.
It is a real bonus when you have two identical machines next to each other. I would take readings with a IR Thermometer on several locations around the machine, including all the cylinders. One leaking valve can cause this. I assume the heads are water cooled so the temps there are not of much use. The IR Thermometer will also double check the discharge temps.
If I found nothing, I would shut off the machine and close the Suction Valve. If a discharge valve or the bypass valve is leaking the pressure will climb quite rapidly. You do not have to, and it might not be wise to let the crankcase pressure rise to full head pressure doing this.

Am Snowbound today so will look forward to your report:)

[US Iceman]

If I found nothing, I would shut off the machine and close the Suction Valve. If a discharge valve or the bypass valve is leaking the pressure will climb quite rapidly.


Hi NH3LVR,
That's always a very good way to see if the discharge valves or internal relief valve is leaking.

You also raise a good point about the possibility of only one broken discharge valve being the culprit. Sometimes you can feel the cylinder temperatures in order to track down the offending area too. You sure can't tell anything by the head temperatures with the water cooled jackets present.

I've seen both of these before, and the best way to start out the analysis is as you suggested. Good call!

[SIGNSTU]

Using the ir thermometer the temp are the same every ware I check on both machines. But running the comp. with the suction valve closed, once it shuts down on low suction I closed suction and discharge valves and there was a rapid rise in pressure that tells me valves or bypass. with out doing alot of work and spending alot of money any way of telling, bypass or discharge?

[NH3LVR]

SIGNSTU;

Unfortunately my inexperience with Sabroe prevents me from offering much specific assistance.
A couple of points however.
It is not necessary to close the discharge valve when doing this test. Although there is still pressure above the heads it will soon equalize with the Suction if there is a leak and the discharge is closed.
I would repeat the test on the other machine and compare the two.
It is unlikely that the internal relief is leaking unless it has opened in the past, but it is possible.
One thing I forgot to mention is that it is wise to close the return from the oil separator while testing, if it is leaking it can change your results.
Since I do not know the construction of the Sabroe relief valve I cannot tell you how to test it. If it is installed with a pipe thread it could be removed and tested with air. It should be sufficient to apply enough pressure to simulate or slightly exceed operating differentials. I would not try to open the valve with pressure. That could add to your problems. Relief valves are not always known to reset properly after opening.
Good luck and I wish I could be of more assistance.:)

[US Iceman]

One way to check the internal relief valve is to have someone close off the suction service valve with the compressor running. When the compressor shuts off on low pressure, use a long screw driver to listen to the relief valve.

Put the tip of the screw driver right on top of the area where the relief valve is, with the hard plastic end of the screw driver placed directly on your hear (preferrably the bones close to your ear).

If the relief valve is leaking you should be able to hear it hissing.

If this appears to be OK, then the problem is in one of the discharge valves.

I would concentrate on the compressor with the higher discharge temperature for sure.

Have had any problems with high discharge pressures in the recent past? If so, there might be a stonger possibility of the relief valve lifting, or, if someone started the compressor with the discharge service valve closed.:o

My guess is it's just a single discharge valve that is gone, otherwise if it were several, the temperature would be really high. The same applies to the internal relief valve. If it lifts and the compressor continues to run... I've seen the paint burnt off of the compressors.

[NH3LVR]

One way to check the internal relief valve is to have someone close off the suction service valve with the compressor running. When the compressor shuts off on low pressure, use a long screw driver to listen to the relief valve.

Good suggestion Iceman:)
I forgot to mention this old trick.
I have a medical type stethoscope I use when checking for valve problems. I have a automotive type with a probe as well, but where thing are accessible the diaphragm type works a little better.

[US Iceman]

Peter has mentioned some of these tricks before.

Some of the best "test" instruments we have are our ears, eyes, and hands (taste and smell too, although you have to be careful with these two in ammonia systems:D ).

They may not be extremely calibrated, but they are good enough to help us narrow down the offending area.