Dunham Bush Chiller Alarm

This is a question for any body that can help clear my confusion on a Low Oil Pressure Diff. Alarm on a Dunham Bush Chiller, Mod # IPCX 350-HFALXNP-Q.

The alarm setpoint is 25 psig. It shuts down the Chiller and after the chiller is reset, the Diff. oil pressure starts about 42 then drops as the compressor loads up. Once it gets up to about 95% loaded it has dropped back to about 26-27 psi, then eventually after a couple hours drops below the 25 psi Low Differntial setpoint and shuts down in alarm.

I would understand if it was a high Diff. that it might be the filter. But I can't even find a high Differential setpoint on the chiller screens. Is the low diff. alarm concerning the filter? does it mean that maybe the filter is open, damaged?

I am the Operator at this time on this equipment and any advice would be appreciated. Also material on the chiller is hard to come by aparently, any advice on that would be appreciated also. Thanks...

Hello Regulator do you know what your suction superheat is? could be the expansion valve flooding back causing oil dilution, loss of oil pressure when fully loaded
Regards Dave

Thanks Dave, I am not at work now and will not go back for a few days. I do remember that the Superheat was low, I want to say around 2 Deg. Someone else said the same thing so when I see the Problem again, I will definitly watch the superheat.

if anybody else has any input.....it is appreciated.... Regulator

Some Dunham Bush chillers have electronic expansion valves (24v Danfoss) and superheat is set at 3deg C. The suction pressure is measured with a transducer and this is then converted to a saturated vapour temperature by the software. Superheat can then be determined. With this type of control, liquid floodback is not normally a problem.

Has the chiller got an oil seperator?, if so then check that the gravity oil return is working ok - a silly question but is the oil level correct?

frank

Hi Regulator:)
what type of compressor are we talking about, piston or screw:confused:
In the meantime, don't reset the compressor until a fault can be determined. What about the operation and maintenance manual, what does it say.
Regards. Andy:)

hello Andy, it is a screw with liq. injection, Haven't got my hands on the manual yet. thanks

Hi Regulator:)
low diff oil pressure on a screw can be a number of things. You would have to establish what way you oil pressure is generated, there are four common configurations.
1/ Continuously running oil pump which is separate from the main compressor, with it's own drive motor.
2/ Pre-lubrication oil pump which is as above, but only runs for a few minutes at start-up to establish oil pressure.
3/ Inbuilt oil pump, driven off the main compress or drive.
4/ No oil pump; differance between inlet and outlet (suction and discharge) creates the driving force for the oil (ol pressure is differance, less pressure drop in the oil piping and the oil filter)

The most common is the latter. When you have established what you have, the problem will become clearer.
If and only if you have the latter lubrication system, look for the following:
Low head pressures and high suction pressures, this will cause low oil diff.
If as I suspect you have a low head, elevate the head pressure, ie. the condenser fan settings (or just switch they off on initial start up until say 40 deg C condensing is developed). This will initially create the oil pressure until the refrigeration load is applied to the condenser, after which the oil diff will be self maintaining.
Regulator you also talked off low suction supheat, this is also possibly a product of low head pressure, to be correct the electronic valves are opening up to establish themselves, initially, with low head they have to open up to a high opening %, the head pressure then starts to establing rather rapidly, with the capacity of the valves increasing rapidly too and the electronic system has lag which alllows refrigerant carryover.
Hope this helps. Regards. Andy:)

update
The problem went away while I was away from work. The only thing I know for sure that they did to it was replace the oil filter. The thing it has been doing lately is cycling the hot gas bypass solenoid almost constantly, any ideas on this?

just another update, the HGBP was cycling so much because the Suction pressure transmitter was not functioning properly. After it got shut down for maintenance, it would not restart because it was reading below the low suct. cutoff.

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