3.2 Piping Configuration
The inlet piping from the compressor to the
separator should follow a few simple rules:
1. The discharge header should be one
consistent size throughout.
2. Step changes in the line diameter should
be avoided with the exception of the
reducing fittings required to couple to
the oil separator.
To optimize the performance of the separator,
it should be piped with a 90° elbow in the
discharge line just prior to entering the oil
separator as shown below.
Inlet piping to the separator must be sized to
maintain sufficient velocity at the minimum load
condition of the rack. The minimum velocity
should be no less than 20fps (feet per second)
(6.1 mps [meters per second]) and the maxi-
mum velocity should be no more than 75fps
(22.9 mps). Velocities above this limit may
result in excessive pressure drop across the oil
separator.
Steel refrigerant piping should not be used on
screw compressor applications. See section
4.1 for further details.
3.3 System Oil Charge
The system oil charge will vary depending
on the size of the separator used, size of the
oil cooler (where applicable), oil manifolding,
and natural refrigerant piping traps and coat-
ing. The nominal oil charge for a three com-
pressor parallel rack is approximately 10–20
gallons (28.5–57 liters), but may vary
significantly.
The oil charge (i.e. quantity required to fill to
the top sight glass) for the smaller single
compressor oil seperator is approximately
5 gallons, while it is 10 gallons for the larger
separator.
See section 9.1 for the recommended oil
charging procedure.
The screw compressors have no oil sump and
therefore are shipped empty and must not be
charged. For the recommended oil type,
please refer to Section 1.4.
Carlyle recommends operating the system with
the oil level between the top two sight glasses
on the oil separator.
3.4 Oil Level Switch
An oil level switch is required and must be
located in the bottom of the oil separator or
reservoir. The level switch is used to monitor
the oil level and act as a safety in case of low
oil levels.
The float switch must be wired to
open all the compressor control circuits
on the rack during cases of low oil level.
The float switch will be normally closed when
adequate oil is in the separator or reservoir
sump.
This device is 240v pilot duty and
rated for 20 VA maximum.
During transient
conditions, the oil level switch may rapidly
fluctuate causing nuisance tripping. To avoid
this, the level switch may be controlled by the
rack controller with the following logic:
DEFINITIONS:
OIL_LEVEL
PROGRAM VARIABLE
OIL_LEVEL =1
OIL LEVEL OK
OIL_LEVEL = 0
OIL LEVEL FAULT
FLOAT PROGRAM COUNTER VARIABLE
LEVEL PROGRAM VARIABLE TO INCREMENT/DECREMENT
COUNTER
LEVEL = 1 OIL LEVEL OK
LEVEL = -1 OIL LEVEL FAULT
PROGRAMMING:
INITIALIZATION BLOCK
FLOAT = 3
PROGRAM BLOCK
READ OIL_LEVEL
LEVEL = 2*(OIL_LEVEL - .5)
~CONVERTS 1 OR 0 TO 1 OR -1
FLOAT = FLOAT + LEVEL
IF (FLOAT = 0) THEN SHUTDOWN COMPRESSOR(S)
IF (FLOAT>3) THEN (FLOAT = 3)
~LIMIT FLOAT TO MAXIMUM OF 3
REPEAT PROGRAM BLOCK EACH 15 SECONDS
This Anti-Cycling algorithm will keep a
running tally of the oil level switch status.
The algorithm reduces the likelihood of
nuisance tripping at low oil level.
Another method to avoid nuisance trips is to
add a 30-second time delay to the oil level
switch control circuit. (After a trip, a 2-minute
time delay may be incorporated before
attempting to restart.)
12
OUTLET
INLET