Gulf+Western ACWC-SC - Slide Valve Unloading System

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SLIDE

VALVE

UNLOADING

SYSTEM

1 ne

tlonn

screw

compressor

capacity

control

system

for

infinite

modulation

consists

of

a

slide

valve and

hydraulic

piston

/

cylinder

operator

internal

to

the

compressor;

plus

three

hydraulic

solenoid

valves (UL-1,

UL-2

&

UL-3)

piped

externally.

The

slide

valve

forms

a

portion

of

the

chamber

wall in

which

the

rotors

turn;

thus,

its

position

with

respect

to

the

rotors

determines

the

effective

rotor

length

and

thereby

the

percent

of

full load

capacity

.

Upon

compressor

start-up

,

UL-3

is opened.

This

allows

oil pressure

to

act

upon

the

hydraulic

piston,

holding

it in

the

fully

unloaded

position

.

After

30 seconds,

during

which

time

full

oil

flow

is

established

to

all

bearings

surfaces,

UL-3

is

closed

.

At

this

point,

the

temperature

controller

is free

to

open

and close UL-1

or

UL-2

in

response

to

the

supply

water

temperature

.

The

slide

valve

will

move

to

the

left

(loading)

by

force

of

discharge

pressure

,

whenever

UL-1

opens

to

permit

flow

to

the

oil

return

(low

Load

Unload

¢::J

c::>

Oil Pressure

Slide Valve

Oil

Pressure Lines

Screw

Rotor

pressure) line.

The

slide

valve

will

move

to

the

right

(unloading)

whenever

UL-2

opens

the

oil

supply

(high

pressure) line,

since

the

force

of

the

oil

exceeds

that

of

the

discharge

gas.

The

temperature

controller

sends a series

of

power

(energizing)

"

pulses

"

to

the

appropriate

solenoid

to

adjust

to

load

conditions

.

The

further

the

supply

water

temperature

is

from

the

controller

set

point,

the

longer

is

the

duration

of

the

pulses.

The

series

of

pulses

will

continue

until

the

controller

is satisfied. As

the

water

temperature

approaches

the

set

point

,

the

pulses

become

quite

brief

to

prevent

overshooting

the

set

point.

This

method

of

compressor

unloading

in

conjunction

with

supply

water

sensing

minimizes

action

/

reaction

lag

time

and

overshoot

resulting

in an

exceptionally

precise

and

stable

control

of

supply

water

temperature

.

UL-1

Oil

Return

Hydraulic

Piston

Oil

Supply

Vent

to

Suction

The

following

table

lists

solenoid

valve

position

for

all

three

operating

modes.

UL-1

UL-2 UL-3

Starting

Close

Close

Open

Loading

Open

Close

Close

Unloading

Close

Open

Close

4

r

~

'-...../'

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