Emerson VSG, VSSG manual 3. Troubleshooting Guide - General Problems & Solutions 1 of

Section 6 • Troubleshooting

Table 6-3. Troubleshooting Guide - General Problems & Solutions (1 of 3)

Problem

Solution

	•	After failing to start compressor with “Prelube Oil Pump Inhibit”, first allow
		Discharge pressure, Oil Filter In pressure and Out pressure to equalize. Then
		restart compressor. If compressor fails to start due to low oil pressure, contin-
		ue troubleshooting with items below.
	• Reset Prelube Oil Pressure Setpoint in Alarms and Trip Setpoints screen to
		lowest recommended setpoints.
	• Check calibration of oil manifold transducer, discharge pressure transducer,
		and suction transducer.
Low Oil Pressure at Start	• Check for correct oil pump motor rotation and operation.
	• Ensure transducer isolation valves are open.
	• Verify that the correct transducer ranges are selected.
	• Check to see all oil line valves are open except the oil dump valve used to fill
		the lines and oil cooler.
	• Check oil strainer for dirt.
	• Check oil filter pressure drop.
	• Check “Prelube Oil Pump Time Limit” setpoint is sufficient in Compressor
		Timer Setpoints screen.
	• Prelube pressure is manifold pressure minus discharge pressure.
	• Check solutions in “Low Oil Pressure at Start”.
	• Check that there is proper discharge pressure ratio to create differential pres-
		sure, otherwise oil pressure can’t be maintained. Oil pressure is manifold oil
		pressure minus the suction pressure. It is a net pressure.
Low Run Oil Pressure	• If the oil pump is selected to be a part time oil pump in the “Setup” menu,
		then ensure that it only shuts off at an appropriate pressure ration that takes
		into account pressure drops through the oil cooler. This is a set point in the
		“Compressor Control Setpoints” menu called “Oil Pump Restart.” It is a pres-
		sure ratio. (discharge pressure in psia/suction pressure in psia) Default ratio
		is a pressure ratio of 3.00:1 that stops the pump and 2.80:1 that restarts the
		pump. This ratio can be increased. Do not decrease without consulting Vilter.
	• Clean oil strainer screen.
	• Change oil filter, maybe plugged or collapsed.
Oil flow or oil pressure	•	Oil pump gears worn internally, excessive end-clearance.
problems	•	Oil priming valve used on air-cooled cooler units is open.
	• Relief in-line check valve stuck open.
	• Pressure ratio too low, oil pump should be on.
	• Check that the correct pressure or temperature range is selected in the
Faulty pressure or temperature		Instrument Calibration menu.
	• Check cable connections at device, terminal strips, and PLC input card for
readings
		correct wiring and shielding (RF noise).
	• Check calibration of RTDs and transducers.

VSG/VSSG • Installation, Operation and Maintenance Manual •Vilter/Emerson • 35391SSG 6 – 5