Solenoid Valve Basics. What is a solenoid valve? Click here to read the definition. What are the different parts of a solenoid valve? Solenoid valve technology in particular that B. It is one of the main pillars of our company success.A solenoid valve is an electromechanically operated valve. The valve is controlled by an electric current through a solenoid: in the case of a two-port valve the flow. A solenoid valve is a combination of two basic. Solenoid Valves Principles of Operation Solenoid Valves EngineeringR2. 4 ENGINEERING 448 1 Cyl. We would like to show you a description here but the site won’t allow us. The illustration below depicts the basic components of a solenoid valve. The valve shown in the picture is a normally- closed, direct- acting valve. This type of solenoid valve has the most simple and easy to understand principle of operation. Orifice. How does a solenoid valve work? The media controlled by the solenoid valve enters the valve through the inlet port (Part 2 in the illustration above). The media must flow through the orifice (9) before continuing into the outlet port (3). The orifice is closed and opened by the plunger (7). The valve pictured above is a normally- closed solenoid valve. Normally- closed valves use a spring (8) which presses the plunger tip against the opening of the orifice. The sealing material at the tip of the plunger keeps the media from entering the orifice, until the plunger is lifted up by an electromagnetic field created by the coil. The video animation below shows the operation sequence for a direct- acting solenoid valve. Understanding Solenoid Valves. The solenoid assembly consists of a coil, plunger, and sleeve assembly. In a normally closed valve, a plunger return spring holds the plunger against the orifice, preventing flow through the valve. When the coil is energized, a magnetic field is produced, raising the plunger and allowing flow through the valve. In a normally open valve, when the coil is energized, the plunger seals off the orifice, stopping flow through the valve. Safe Working Pressure — The maximum pressure a valve may be exposed to without experiencing any damage. Solenoid Valve Basics. What is a solenoid valve? Click here to read the definition. What are the different parts of a solenoid valve? The illustration below depicts. The valve does not have to be operable at this pressure, but merely withstand the pressure without damage. Solenoid Valve Applications: Evaporator Temperature Control A solenoid valve installed in the liquid line as close to the evaporator as possible, in conjunction with a narrow differential thermostat, is an excellent temperature control. By mounting the thermostat bulb in the supply or discharge air across the evaporator, the temperature swing is limited only by the differential of the thermostat. This type of temperature control can be used on a single or multiple evaporator system and is particularly useful on multiplexed systems with evaporators at different temperatures. Defrost Pump Down In situations where the condensing unit is installed in a low ambient, such as on a rooftop in northern climates, and the evaporator is operating at a temperature above the ambient, a pump down solenoid valve should be used. This allows the pressure control to be set at a cut out of 1 to 2 psi and the cut in to be set at a pressure below the pressure corresponding to the ambient temperature. This will ensure that the condensing unit will start after cooling down during the defrost. When a system has a defrost pump down solenoid valve, a thermostat should be used in series with the defrost time clock to control the temperature of the space or fixture. An alternative to the thermostat would be an evaporator pressure regulator. Note: System diagrams are for illustrative purposes and are intended to show application of solenoid valves only. Heat Reclaim Systems Basically, there are two types of heat reclaim systems: the series system and the parallel system. In the series system, during normal operation, the discharge gas is condensed completely in the condenser. During the heating mode, the normally opened solenoid valve closes off the condenser and the normally closed solenoid opens to allow the discharge gas to flow into the heat reclaim coil. Complete condensation can occur in the heat reclaim coil if so designed, but manufacturers often prefer to take advantage of all the sensible heat available but only part of the latent heat, depending on the condenser for complete condensation. In the parallel systems there are, in effect, two separate condensers. During normal operation, the condenser is used for complete condensation of the discharge gas. In the heat reclaim mode the discharge gas is completely condensed in the heat reclaim coil, thus maximizing the use of both sensible and latent heat. Some manufacturers recommend installing a 1/4- inch line from the heat reclaim coil, at its lowest point, back to the receiver to ensure the proper drainage of oil and liquid refrigerant during the off cycle. Other manufacturers suggest the installation of a pressure control, to ensure that the system will switch from the heat reclaim mode to the condenser in the event of fan stoppage or clogged filters. Split Evaporator — Humidity Control There are often times when the air temperature is satisfactory but the humidity level is too high. This can be remedied by using only half the evaporator to dehumidify the air without excessive cooling and the addition of auxiliary heat. This can best be accomplished by using a normally open solenoid valve on one half of the evaporator controlled by a humidistat. Hot Gas Defrost System Hot gas defrost offers an excellent alternative to electric or air defrost. In this system the hot compressor discharge gas is routed to the outlet of the evaporator. This hot gas warms the evaporator, thaws any frost that has accumulated, condenses into a liquid, and flows into the common liquid line to feed the other evaporators. In order for this system to work properly, check valves must be installed to allow flow around the expansion valves. A pressure reducing valve should be used in the liquid line to provide a pressure differential between the condensed refrigerant leaving the defrosting evaporator and the common liquid line. The system shown is drawn with only two evaporators but it is recommended that only 2. An alternative to the hot gas defrost system is the cool gas defrost, which uses the gas from the top of the receiver to defrost the evaporators. Because the cool gas defrost operates at a lower temperature, the thermal expansion of the refrigeration lines is reduced. This often eliminates the need for special piping techniques and leaks caused at line connections by excessive thermal flexing. Capacity Control System A simple method of providing compressor unloading is to use a solenoid valve connecting the discharge and suction lines of the compressor. The solenoid valve is controlled by a pressure control which responds to suction pressure. When the switch closes, it opens the normally closed solenoid valve and discharge gas is short circuited back to the suction side of the compressor. In order to prevent overheating of the compressor, a thermostatic expansion valve should be installed to provide cooling to the compressor suction gas. An alternative method consists of injecting hot gas into the evaporator inlet. This prevents overheating of the compressor and increases the velocity of the gas through the evaporator. This type of unloading should not be attempted without thorough analysis of solenoid valve and expansion valve sizing. Liquid Line Shut- Off In an effort to obtain a higher efficiency rating on residential and commercial air conditioning systems, a normally closed solenoid valve typically is installed in the liquid line located near the air handler or furnace. In this case, the solenoid valve is wired in parallel with the contactor circuit (2. VAC) and may require a larger transformer to accommodate the valve. As an alternative method, a normally closed solenoid valve may be located in the liquid line near the condensing unit and wired directly to the compressor motor terminal box. This solution improves system efficiency and maintains the refrigerant charge in the condenser coil during the off- cycle of the compressor which prevents refrigerant migration when long piping runs are used. If the application requires a fail- safe or open mode, a normally open solenoid valve may be used. In this instance, the valve may also be located in the condensing unit and wired in series with the compressor crankcase heater. Compiled by the Parker Hannifin Corporation Engineering Staff, New Britain, Conn. For more information, visit www. Publication date: 0.
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