Pressure & Temperature regulating valves
Pressure and Temperature Regulators –Type SPM And Pilot Valves
Main valves, type SPM 1 and SPM 3 Main valve types SPM is specially developed to regulate pressure and temperature in refrigeration, freezing and air conditioning plants with fluorinated refrigerants and ammonia. SPM is a pilot operated main valve with screwed-in pilot valves or pilot valves mounted in an external pilot line. Main valves types SPM are used in refrigeration plant with dry evaporation, pump circulation, natural circulation. The regulator is available in two variants, SPM 1and SPM 3. SPM 1 is designed to accept one pilot valve either screwed-in or mounted in an external pilot line. SPM 3 will accept three screwed-in pilot valves or pilot valves mounted in an external pilot line. Thus several functions can be performed by the same valve. PILOT VALVES: Pilot valve program contains : Pressure controlled pilot valve type SCVP LP Pressure controlled pilot valve type SCVP HP Pressure controlled pilot valve type SCVC with pilot signal connector Differential pressure controlled pilot valve type SCVPP (LP) Differential pressure controlled pilot valve type SCVPP (HP) Solenoid pilot valve type SVM-NC and SVM-NO The pilot valves can perform the following functions: Constant pressure regulation Capacity regulation Crank case pressure regulation Refrigerant pressure regulation
Pilot Control Modules
Pilot valve program contains: Pressure controlled pilot, valve type CVP(LP), Pressure controlled pilot, valve type CVP(HP), D i ffe re n ti a l p re ssu re controlled pilot valve, type CVPP(LP), D i ffe re n ti a l p re ssu re controlled pilot valve type CVPP(HP), Solenoid pilot valve type EVM-NC and EVM- NO, The pilot valves can perform the following functions. Constant pressure regulation, Capacity regulation, Crank case pressure regulation, Refrigerant pressure regulation.
Discharge Gas Bypass Valves
Discharge Bypass Valve is used to bypass a portion of the hot discharge gas directly into the low side to limit the minimum evaporating pressure during periods of low load either to prevent coil icing or to avoid operating the compressor at a lower suction pressure than it was designed to operate. This valve, which opens on a decrease in suction pressure, can be set to automatically maintain a desired minimum evaporating pressure regardless of the decrease in evaporator load.
SYSTEM CAPACITY CONTROL: On many air conditioning and refrigeration systems it is desirable to limit the minimum evaporating pressure during period so flow load either to prevent coil icing or to avoid operating the compressor at a lower suction pressure than it was designed to operate. Various methods have been used to achieve this results such as integral cylinder unloading, gas engines with variable speed control, or multiple smaller systems. Compressor cylinder unloading is used extensively on larger systems but is too costly on small equipment, usually 10hp and below.
Cycling the compressor with a low-pressure cut out control has had wide spread usage but is being re-evaluated for three reasons.
1. On-off control on air conditioning systems is uncomfortable and does a poor job of humidity control.
2. Compressor cycling reduces equipment life.
3. In most cases, compressor cycling is not economical because of peak load demand charges.
One method that offers a practical and economical solution to the problem is to bypass a portion of the hot discharge gas directly into the low side. A modulating control valve, commonly called a Discharge Bypass Valve, does this. This valve, which opens on a decrease in suction pressure, can be set to automatically maintain a desired minimum evaporating pressure regardless of the decrease in evaporator load. Manik manufactures Discharge Bypass Valves to meet this demand.
OPERATION: Manik Discharge Bypass Valves (DBV) responds to changes in down stream 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 stroke is reached.
