Heatcraft Refrigeration Products H-IM-72A User Manual download pdf (Page 31)

Liquid Drain Control Method

This method is ideal for large capacity systems since a

smaller regulator is required for liquid line than for discharge

line.

During warm ambient temperature conditions valves A and C

will be open and Valve B will be closed. When the ambient

temperature at the condenser drops, the condenser pressure

will tend to become lower. As this pressure is reduced, when

the pressure becomes as low as its setting, Valve A will begin

to close, thus causing the refrigerant to back up inside the

condenser tubes, reducing the condensing surface and

allowing the pressure to be maintained. As Valve A closes,

the receiver pressure may be reduced by the cold entering

liquid to a level below the setting of Valve B, which will begin

to open to bypass sufficient gas to maintain the receiver

pressure at the set point of Valve B. Check valve C will

prevent the high pressure from backing up to the condenser

when the receiver pressure is higher than the condenser

pressure, as would be the case during shutdown in a system

with a warm receiver.

When the condenser pressure builds up to the setting of

Valve A, it will open allowing liquid to flow to the receiver.

To describe it again, during cold ambient temperature

conditions this liquid will be considerably subcooled and will

tend to lower the receiver pressure. Valve B will sense the

drop in pressure and open to admit hot gas into the drain line,

thus pressurizing and warming the liquid and maintaining the

receiver pressure.

Recommended Valve Settings

Regulators ordered for a Condenser Pressure Control system

for use with common refrigerants will be furnished with the

ranges and factory settings shown in Table 29 below. Turning

the adjusting stem in (clockwise) will raise the set point;

turning the stem out (counterclockwise) will lower the set

point. See Table 29 below for ranges and amount of

pressure change per turn.

Table 29. Pressure Range, Set point & Change per Turn

Factory

Valve Range Set Point Change Per Turn

Type psig kg/cm

psig kg/cm

A4A

75 to 5.2 to

140 9.8 53 3.7

ARA0 280 19.7

A7A 75 to 5.3 to

A7A1 D 280 19.7 120 8.4 75 5.3

A72

A9 B

80 to 5.6 to

120 8.4 25 1.8

220 15.5

Field Adjustment

Before final field adjustment of regulators for Condenser

Pressure Control, the following should be done:

1. Install gauges to read compressor discharge, condenser

and receiver pressures.

2. Fully charge the system.

3. Have other controls and components functioning

properly.

4. Have the system as fully loaded as possible.

5. Final adjustments should be made when the outdoor

ambient is below 65°F. Ideally the ambient should be

near minimum system outdoor temperature to allow the

system pressures to drop below the regulator pressure

settings. Before adjusting make sure that all manual

opening stems on the regulators are set for automatic

operation. It may be necessary to temporarily deactivate

the low pressure cut out controls to keep the compressors

running during adjustment.

6. The regulators should be preset using information in

Table 29.

7. When the valves are adjusted with the system operating,

enough time must be allowed for the system to stabilize.

Check the sight glass to make sure sufficient liquid is

supplied to the evaporators.

8. Turn the condenser fans off to allow the discharge

pressure to build up. The regulator A should be adjusted

to open when the pressure reaches the desired control

point. Listen for flow through regulator A while watching

the pressure gauge.

To determine the final setting of regulator B, allow the

condenser fans to run long enough to subcool the liquid

supplied to the receiver. Adjust the regulator until the desired

receiver pressure is obtained. Flow through the valve can be

determined by listening at the valve for gas flow or by feeling

the outlet for change in temperature. The setting of regulator

B should be at least 10 psi lower than the setting of regulator

Hot Gas Bypass Regulator

Adjustment

Discharge Bypass Valves (DVB) respond to changes in

downstream or suction pressure. When the evaporating

pressure is above the valve setting, the valve remains closed.

As the suction pressure drops below the valve setting, the

valve responds and begins to open. as with all modulating

type valves, the amount of opening is proportional to the

change in the variable being controlled - in this case the

suction pressure. As the suction pressure continues to drop,

the valve continues to open farther until the limit of the valve

stoke is reached.

On refrigeration systems discharge bypass valves are used to

prevent the suction pressure from going below the minimum

value determined by the job requirements.

Sporlan Valve Company

Valve Setting and Adjustment

A complete discussion on valve settings is given in Sporlan

Application Bulletin 90-40. The fully adjustable models

ADRS(E)-2, ADRP(E)-3, and ADRH(E)-6 are available with

two adjustment ranges - 0/30 and 0/80 psig. The standard

factory settings for these are 20 and 60 psig, respectively.

The ADRI(E)-1-1/4 is available with a 0/55 psig range and the

standard factory setting is 28 psig.

To adjust these valves, remove the cap an turn the

adjustment nut with a 5/16” hex wrench for fully adjustable

models ADRS(E)-2, ADRP(E)-3, and ADRH(E)-6. The

ADRI(E)-1-1/4 model has a 3/8” adjustment screw on top of

the adjustment housing. A clockwise rotation increases the

setting and a counterclockwise rotation decreases the setting.

1 2 ... 26 27 28 29 30 31 32 33 34 35 36

Comments to this Manuals

No comments

Heatcraft Refrigeration Products H-IM-72A User Manual Page 31

Comments to this Manuals

Related products and manuals for Air compressors Heatcraft Refrigeration Products H-IM-72A