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ManualsBrandsSiemens ManualsControl Valves7/8" 2-Port PS43 Modulating Refrigerant Valve with Magnetic Actuator (5 Cv)

M3FB…LX… Series Modulating Control Valve Technical Instructions

for Hot Gas Control Document Number CA2N4721E-P25

December 4, 2019

Siemens Industry, Inc. Page 7

Application

Examples

The diagrams shown here are examples only, without installation-specific details.

Three-way Hot-gas

Bypass Control

• For accurate control of evaporators, from 0 to 100% refrigeration capacity.

• Suitable for test rooms, laboratory systems, small chilled water units and DX

evaporators with a refrigeration capacity of up to approximately 11.4 tons (40 kW).

• Recommended pressure drop pv100 across the fully-open valve (control path

AB → A): between 7.2 and 14.5 psi (see Figure 1).

Example:

Refrigeration capacity Qo

Refrigerant

Condensation temperature tc

Evaporation temperature to

Liquid temperature tfl

Selected valve

Pressure differential pv across

valve

6.8 tons

R22

104°F (40°C)

41°F (5°C)

95°F (35°C)

M3FB15LX/A

10.2 psi (0.7 bar)

Figure 5. Three-way Hot-Gas Bypass Control Application.

Indirect Hot-gas Bypass

The control valve throttles the capacity of a compressor stage. The hot gas is injected

directly into the evaporator allowing capacity control from 100% to approximately 0%.

• Suitable for use in large refrigeration systems in air conditioning applications to

prevent unacceptable fluctuations in temperature between compressor stages.

• The pressure differential pv100 across the fully-open valve is determined by the

condensation pressure at low load minus the pressure upstream of the evaporator.

• If details are not provided, the pressure differential pv100 can be assumed to be

58 psi (4 bar).

Example :

Refrigeration capacity Qo of one

compressor stage

Refrigerant

Condensation temperature full

load/low load

Evaporation temperature full

load/low load

Liquid temperature tfl

Pressure differential pv

(from R22 vapor table)

Selected valve

Actual capacity

8.5 tons

R22

113/95°F (45/35°C)

41/59°F (5/15°C)

104/86°F (40/30°C)

81 psi (5.6 bar)

M3FB15LX/A

Approx. 40 kW

M3FB15LX/A

Approx. 40 kW

Figure 6. Indirect Hot-gas Bypass Application.