Monthly Archives for January 2011

Automatic-expansion valve

The automatic-expansion valve controls liquid flow by responding to the suction pressure of the unit acting on its diaphragm or bellows (see Fig. 11-2). When the valve opens, liquid refrigerant passes into the evaporator. The resulting increase in pressure in … Continue reading

16. January 2011 by admin
Categories: Controlling Refrigerant | Tags: , | Leave a comment

Hand-expansion valve

Of the several types of metering devices. the hand-expansion valve is the simplest (see Fig. 11-1). Used only on manually controlled installations, the hand-expansion valve is merely a needle valve with a fine adjustment stem. When the machine is shut … Continue reading

16. January 2011 by admin
Categories: Controlling Refrigerant | Tags: | Leave a comment

Electric-compensating back-pressure regulator

usually found at the top of the regulator. In an electrically compensated regulator, turning the stem to obtain different refrigerant pressures and temperatures in the evaporator is accomplished by a small electric motor. This motor rotates the adjusting stem in … Continue reading

16. January 2011 by admin
Categories: Evaporators | Tags: | Leave a comment

Air-compensating back-pressure regulator

A standard regulator is reset by manually turning the adjusting stem, which increases the spring pressure on top of the diaphragm. In an air compensated regulator, a change of pressure on top of the diaphragm is accomplished by introducing air … Continue reading

16. January 2011 by admin
Categories: Evaporators | Tags: | Leave a comment

Refrigerant-powered compensating-type pilot valve

The upper portion of the valve head is similar to a standard pressure regulating head. On the lower portion of the head another diaphragm is connected to the main diaphragm by a push rod. As the thermal bulb warms, the … Continue reading

16. January 2011 by admin
Categories: Evaporators | Tags: | Leave a comment

HVAC Back-Pressure Regulator Applications of Controls

In a refrigeration system designed to maintain a predetermined temperature at full load, any decrease in load would tend to lower below fullload temperature the temperature of the medium being cooled. To maintain constant temperatures in applications having varying loads, … Continue reading

16. January 2011 by admin
Categories: Evaporators | Tags: | Leave a comment

Valves and Controls for Hot-Gas Defrost of Ammonia-Type Evaporators

The following valves and controls are used in the hot-gas defrost systems of ammonia-type evaporators: Hot-gas or pilot-solenoid valve. The valve is a 1/8 in. ported solenoid valve. It is a direct-operated valve suitable as a liquid, suction, hotgas, or … Continue reading

16. January 2011 by admin
Categories: Evaporators | Tags: , , , , , , , , , , , , | Leave a comment

HVAC Dual-Pressure Regulator

Adual-pressure regulator is shown in Fig. 10-24. It is used on a shell-andtube cooler. The dual-pressure regulator is particularly adaptable for the control of shell-and-tube brine or water coolers, which at intervals may be subjected to increased loads. Such an … Continue reading

16. January 2011 by admin
Categories: Evaporators | Tags: | Leave a comment

HVAC Year-Round-Automatic Constant Liquid Pressure Control System

The constant liquid control system is a means of increasing the efficiency of a refrigeration system that utilizes air-cooled, atmospheric, or evaporative condensers (see Fig. 10-23). This is accomplished by automatically maintaining a constant liquid pressure throughout the year to … Continue reading

16. January 2011 by admin
Categories: Evaporators | Tags: , | Leave a comment

Low-temperature ceiling blower

The low-temperature liquid recirculating system illustrated in Fig. 10-22 uses several controls. During the cooling cycle, Number 1 pilot valve is opened and Number 2 pilot valve is closed, holding the gas-powered solenoid valve wide open. This allows flow of … Continue reading

16. January 2011 by admin
Categories: Evaporators | Tags: | Leave a comment

← Older posts

Newer posts →