Carlyle 05T-048 Toepassingshandleiding - Pagina 9

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3.0 Oil Management System

3.1 Oil Separator

An oil separator is required on all Carlyle screw compressor

systems. The screw compressors do not have an oil sump

for storage of the system oil charge. The selection of the oil

separator should consider the desired oil circulation rates as

well as storage of oil for the entire bank of compressors.

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 vortex separators, they

should be piped with a 90° elbow in the discharge line (turn-

ing in the same direction as the vortex) just prior to entering

the oil separator.

Inlet piping to the separator must be sized to maintain

enough 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 maximum

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 oil piping is not recommended for use with 05T/06T

screw compressor applications.

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

manifold, and natural refrigerant piping traps and coating.

3.4 Oil Level Switch

An oil level switch is required and must be located in the bot-

tom 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 com-

pressor control circuits on the rack during cases of low oil

level. The float switch will be normally closed when ade-

quate oil is in the separator or reservoir sump. The oil level

switches are generally pilot duty devices, their electrical

switching capacity should be validated to ensure they are

not overloaded. During transient conditions where signifi-

cant foaming is present in the oil sump, the oil level switch

may rapidly fluctuate causing nuisance tripping. System

controls must be designed to discriminate these nuisance

conditions from real low oil level conditions.

3.5 Oil Pressure Protection

The 05T/06T screw compressors are lubricated using oil fed

from the high pressure side of the system. To ensure ade-

quate lubrication the pressure of the oil feed to each com-

pressor must be a minimum of 45psi (3 bar) above suction

pressure. Care should be taken to avoid large pressure

drops between the oil separator (discharge pressure) and

this oil feed to the compressor (oil pressure). See Section

3.9 for addition details on these pressure drops.

The LonCEM protection module provides comprehensive

oil pressure protection through the use of discharge pres-

sure, oil pressure and suction pressure transducers to mon-

itor operating pressures.

Refer to the LonCEM Installation and Operations Guide for

a complete description of the application and operation of

the LonCEM module.

3.6 Oil Solenoids

A normally closed solenoid is required in the oil feed line to

each compressor, see Section 3.12 for oil system schemat-

ics. To avoid excessive pressure drop, the internal port size

must be 5/16 in. diameter or larger. An oil strainer is re-

quired before each oil solenoid (or as an integral part of the

solenoid). The solenoid will protect the compressor from be-

ing filled with oil from the high pressure oil feed line during

the off cycle. Each solenoid must be properly wired to the

Carlyle LonCEM (per installation instructions) of the com-

pressor it is controlling. The valve must be open during the

on cycle and closed during the off cycle. Manually adjust-

able valves must be checked to ensure the manual opera-

tion stem is completely back seated (ensuring the valve is

closed when the solenoid is de-energized).

CAUTION

When testing the control circuit without the compressor

running, the oil line must be valved off so that the com-

pressor will not be filled with oil.

Whenever possible use control logic to determine that the

compressor is running before opening the oil solenoid.

3.7 Discharge Temperature Control

The 06T semi-hermetic screw compressors can be operat-

ed for most applications without external oil cooling. 05T

open drive screw compressors require external oil cooling

any time the system discharge temperature may exceed

180°F(82°C). The CARWIN Selection Software can be

used to estimate the discharge temperature for a given ap-

plication. The CARWIN tool allows for selections to be made

with or without an oil cooler.

See Operating Envelopes in Section 2.1 for operating condi-

tions that may require the use of external oil cooling.

An external oil cooler will reduce both the discharge and

motor temperatures within their respective limits, however,

additional refrigerant injection may still be required. For

screw compressors this injection is either by the motor cool-

ing valve and/or at the rotor injection port. Because refriger-

ant injection for motor and discharge cooling flows into the

screw rotor chamber after the suction gas is trapped, com-

pressor capacity is not significantly affected. Under some

conditions the motor cooling valve alone can accommodate

this extra cooling requirement. For conditions requiring addi-

tional discharge temperature cooling, a desuperheating

valve is recommended. It should be selected to start open-

ing at a discharge temperature of 190°F (88°C) and be fully

open at 200°F (93.3°C). The bulb should be located on the

discharge line within 6 inches (15cm) of the compressor dis-

charge service valve. A properly sized solenoid valve should