must be varied during the setting procedure and it is difficult to determine exactly when the bypass valve opens unless a pressure gauge can be located at the valve outlet.
Therefore, sufficient load must be available in some form to raise the suction pressure above the desired valve setting. Once this is accomplished, the load can be slowly decreased until the DBV opens (a hissing sound and/or an accompanying pressure rise at the outlet connection will indicate that the bypass valve has opened).
Alco Controls
Valve Setting and Adjustment
CPHE and DGRE regulators are commonly used to prevent the suction pressure from falling below a predetermined set point. Complete information about these valves can be found in ALCO CONTROLS Catalog
The first step after installation is to determine the set point for the minimum suction pressure allowable for the application. The following procedure should be followed.
1.Start the system and determine if it is operating properly: Install a gauge on the compressor suction line and measure the suction pressure after the system has stabilized. To make certain that hot gas is not being bypassed, listen to the main regulator flow or feel the outlet piping. If the piping is warm, this would indicate hot gas is flowing.
2.Stop the flow of hot gas by
stem full Counterclockwise.
3.Reduce the evaporator load until the suction pressure lowers to the point at which bypass is desired.
4.If the hot gas solenoid was
5.Turn the power assembly adjusting stem in a Clockwise direction until bypass occurs and suction pressure does not fall below the predetermined set point. A Clockwise turn of the adjusting stem will increase the pressure setting; a Counterclockwise turn will decrease it. Standard pressure pilot is adjustable from 0 to 80 psig, with one complete turn equal to approximately 4 psi change. Adjustments should be made in small increments, allowing for the system to stabilize after each turn.
6.Vary the evaporator load to test at various conditions that the suction pressure does not fall below the predetermined set point.
7.Replace the seal cap on the adjusting stem.
Control Settings
The following tables are for use when mechanical low pressure switches are incorporated for rack pressure control. All control settings are approximate and should be adjusted for actual field conditions and equipment. All settings are based on 10°F TD evaporator.
Installation and Operations Manual
Table 30. Control Settings for R-404A/R-507
Air Temp | EPR | LP C/I | LP C/O |
°F | psig | psig | psig |
69 | 72 | 64 | |
64 | 66 | 57 | |
|
|
|
|
60 | 62 | 55 | |
|
|
|
|
59 | 61 | 53 | |
55 | 58 | 50 | |
|
|
|
|
48 | 50 | 35 | |
|
|
|
|
21 | 24 | 15 | |
20 | 22 | 14 | |
|
|
|
|
15 | 17 | 14 | |
|
|
|
|
12 | 15 | 8 |
Table 31. Control Settings for R-22
Air Temp | EPR | LP C/I | LP C/O |
°F | psig | psig | psig |
54 | 57 | 50 | |
|
|
|
|
50 | 48 | 43 | |
|
|
|
|
47 | 50 | 41 | |
45 | 47 | 40 | |
|
|
|
|
43 | 45 | 38 | |
|
|
|
|
36 | 38 | 25 | |
13 | 17 | 8 | |
|
|
|
|
11 | 14 | 7 | |
|
|
|
|
8 | 10 | 5 | |
5 | 8 | 2 | |
|
|
|
|
Low Pressure Switch Setting for RMCC
Some systems use a form of electronic control such as CPC’s RMCC solid state controller for Rack operation. On these systems, there is one mechanical low pressure control for each suction group that may be on the rack. This control is for backup emergency control in the event of a board or other electronic component failure. This low pressure control must be set for the minimum suction pressure that the rack would be expected to operate at to keep from interfering with the RMCC control.
Example, for a low temperature suction group, this control should be set for 0 - 2 psig cutout and approximately 10 psig cutin. A medium temperature suction group can be set higher. In the event that this control is needed to actually control the compressors, set the cutin and cutout for the suction pressure that you want the compressors to operate to maintain case or box temperatures.
NOTE: This low pressure control will generally be mounted on a compressor with the braided stainless steel tubing connecting to the appropriate suction group header.
32 | Part # 25000102 |
