Unit installation

803 C – 01/05 A – pag. 11/17

Screw compressors

The newest Stargate

single-screw compressor has a well balanced compression mechanism which cancels the

screw rotor load in both the radial and axial directions. Inherent to the basic single-screw compressor design is the

virtually load-free operation, that gives main bearing design life of 3-4 times greater than twin-screws, and

eliminates expensive and complicated thrust balancing schemes. The two exactly opposed gaterotors create two

exactly opposed compression cycles. Compression is made at the lower and upper parts of the screw rotor at the

same time, thus cancelling the radial loads. Also, both ends of the screw rotor are subjected to suction pressure

only, which cancels the axial loads and eliminates the huge thrust loads inherent in twin-screw compressors.

Oil injection is used for these compressors in order to get high COP at high condensing pressure. PFS units are

provided with an high efficiency oil separator to maximise oil extraction.

Compressors have a infinitely variable capacity control down to 25% of its total capacity. This control is made by

means of capacity slides controlled by microprocessors.

Standard start is star-delta type; Soft start type is available (as option) in order to have lower inrush current.

Standard controls

High pressure control

The high pressure switch will shut-down the compressor when the discharge pressure exceeds the setting point

value.

Warning: during testing, stand by the emergency stop switch on control panel, to shut the unit down should the

safety control malfunction. Be sure that the installed gauge is accurately adjusted.

Phase/voltage monitor

The phase/voltage monitor is a device which provides protection against three-phase electrical motor loss due to

power failure conditions, phase loss, and phase reversal. Whenever any of these conditions occur, a contact

opens to the microprocessor which then de-energizes all inputs. When proper power is restored, contacts close

and microprocessor enables compressors for operation. When three-phase power has been applied, the output

relay should close and the "run light" should come on. If the output relay does not close, perform the following

tests:

1. Check the voltages between L1-L2, L1-L3 and L2-L3 (L1, L2, L3 are the three phases). These voltages should

be approximately equal and within + 10% of the rated three-phase line-to-line voltage.

2. If these voltages are extremely low or widely unbalanced check the power system to determine the cause of the

problem.

3. If the voltages are good, using a phase tester, verify that phases are in A, B, C sequence for L1, L2 and L3.

Correct rotation is required for compressor operation. If required to do so by phase sequence, turn off the

power and interchange any two of the supply power leads at the disconnect. This may be necessary as the

phase voltage monitor is sensitive to phase reversal. Turn on the power. The output relay should now close

after the appropriate delay.

System Maintenance

General

To ensure proper operation at peak capacity and to avoid damage to package components, a program of periodic

inspections should be set up and followed. The following items are intended as a guide and are to be used during

inspection and must be combined with sound refrigeration and electrical practicies to ensure trouble-free

performance. The liquid line sightglass indicator on all circuits must be checked to be sure the glass is full and

clear. If the indicator shows that a wet condition exists or if bubbles show in the glass, even with a full refrigerant

charge, the filter-drier element must be changed.