Las válvulas de expansión termostáticas
son desarrolladas para regular la inyección de refrigerante líquido a los
evaporadores. Esta inyección de refrigerante estará siempre regulada por un
elemento termostático que está situado en la parte superior de la válvula de
expansión la cual es controlada en función del recalentamiento del
refrigerante.
Existe una gran variedad de válvulas
de expansión termostáticas, ej: R-22, R 404-A, R-717 (amoniaco). Con puerto
balanceado, con carga MOP. En todas ellas el objetivo es entregar la máxima
eficiencia del evaporador con un sobrecalentamiento adecuado.
Lo primero es analizar y conocer el
funcionamiento de la válvula de expansión: consta de un elemento termostático
(1) separado del cuerpo por medio de una membrana, el elemento termostático
está en contacto con el bulbo (2) a través de un tubo capilar, un cuerpo con un
asiento y orificio (3) y un muelle o resorte.
Funcionamiento
P1: la
presión del bulbo que actúa en la parte superior de la membrana y en dirección
de apertura de la válvula.
P2: la
presión del evaporador, que influye en la parte inferior de la membrana y en la
dirección de cierre de la válvula.
P3: la fuerza
del resorte, que influye en la parte inferior de la membrana y la única
variable que es controlable por parte del técnico.
Cuando la válvula regula, hay un
balance entre la presión del bulbo por la parte superior de la membrana y en
contra se tendrá la presión del evaporador y la del resorte, esto con el fin de
encontrar el sobrecalentamiento más adecuado de operación.
Sobrecalentamiento
El concepto de sobrecalentamiento es
el calor agregado al vapor después de la vaporización en la válvula de
expansión. Esto se puede medir en el lugar donde está el bulbo que es la
tubería de succión. La diferencia que existe entre la temperatura del
termómetro y la presión de evaporación, traducida a temperatura que le corresponde,
el resultado será el recalentamiento en el evaporador, el cual está diseñado
para operar con un rango de recalentamiento de 5° C. Para obtener el
sobrecalentamiento total basta con cambiar el termómetro hasta el final de la
tubería de succión, 30 centímetros antes del compresor, y tomar la presión de
succión a la entrada del compresor. La diferencia en temperatura será el
sobrecalentamiento total el cual no deberá ser mayor a 15° C. Es muy
importante aclarar que estas mediciones se deberán hacer cuando ya se haya
obtenido la temperatura de cámara, si por algún motivo no se llega a la
temperatura deseada se debe revisar bien el balance térmico o probables
taponamientos por suciedad y/o humedad en el sistema de refrigeración.
El sobrecalentamiento sirve para
asegurar que el refrigerante líquido será evaporado en su totalidad en el
evaporador. Pero existen situaciones donde deberá de modificar el ajuste de
sobrecalentamiento, el cual se puede hacer cuando se tienen distancias mayores
a 15mts, en esta condición se podrá disminuir el sobrecalentamiento al girar el
tornillo en contra de las manecillas del reloj. Se recomienda no más de un giro
de 360° con el fin de cuidar el compresor, recordando que el 90% del
enfriamiento de los compresores herméticos está dado por el gas de succión. Por
otro lado, si el sobrecalentamiento total es muy reducido se tendrá que
aumentar el mismo y esto se logra girando el tornillo a favor de las manecillas
del reloj. Cabe aclarar que la presencia o ausencia de escarcha de hielo en una
tubería de succión no indica o garantiza el estado físico del refrigerante.
Válvulas con igualación de presión
externa
Si se usan distribuidores de líquido,
siempre deberán emplearse válvulas de expansión con igualación de presión
externa.
El uso de distribuidores de líquido
causa generalmente una caída de presión de 14.7 psig en el distribuidor y en
los tubos de distribución.
Siempre deberán utilizarse válvulas
de este tipo en instalaciones de refrigeración con evaporadores o
intercambiadores de calor de placas grandes, donde la caída de presión será más
elevada que la presión correspondiente a 2°C.
The thermostatic expansion valves are developed to regulate the injection of liquid refrigerant to the evaporators. This refrigerant injection is always controlled by a thermostatic element which is located at the top of the expansion valve which is controlled as a function of refrigerant superheat.
A variety of thermostatic expansion valves, eg R-22, R 404-A, R-717 (ammonia). With balanced port, loaded MOP. In all of them the goal is to deliver the maximum efficiency of the evaporator with a suitable overheating.
The first is to analyze and explain the operation of the expansion valve: consists of a separate thermostatic element (1) body by means of a membrane, the thermostatic element is in contact with the bulb (2) through a capillary tube, a body with a seat and orifice (3) and a spring.
Result image for thermostatic expansion valve
Performance
P1: bulb pressure acting on top of the membrane and in the direction of valve opening.
P2: evaporator pressure, which affects the bottom of the membrane and in the direction of valve closing.
P3: the spring force, which affects the bottom of the membrane and the only variable that is controllable by the technician.
When the regulating valve, there is a balance between bulb pressure at the top of the membrane and the pressure against the evaporator and the spring will, this in order to find the most suitable operating overheating.
Overheating
The concept of overheating the heat added is steamed after vaporization in the expansion valve. This can be measured in the place where the bulb is the suction pipe is. The difference between the temperature of the thermometer and the evaporation pressure, translated into temperature that corresponds, the result is overheating in the evaporator, which is designed to operate with a range of warming of 5 ° C. For the Total overheat enough to change the thermometer until the end of the suction pipe 30 centimeters before the compressor, and take the suction pressure to the compressor inlet. The difference in temperature will be the total overheating which must not exceed 15 ° C. It is important to note that these measurements should be made when the temperature has already obtained camera, if for some reason it does not reach the desired temperature It should review the thermal balance or probable clogging by dirt and / or moisture in the cooling system well.
Result image for thermostatic expansion valve
Overheating serves to ensure that liquid refrigerant will be fully evaporated in the evaporator. But there are situations where you need to change the setting of overheating, which can be done when you have distances greater than 15m, in this condition may reduce overheating by turning the screw against clockwise. More than 360 ° in order to look after the compressor is not recommended, remembering that 90% of hermetic compressors cooling is given by the suction gas. On the other hand, if the total is very small overheating will have to raise it and this is achieved by turning the screw for clockwise. It should be noted that the presence or absence of frost ice a suction pipe does not indicate or guarantee the physical state of the refrigerant.
Result image for thermostatic expansion valve
Valves with external pressure equalization
If liquid distributors, expansion valves should always be used with external pressure equalization is used.
The use of liquid distributors generally causes a pressure drop of 14.7 psig in the distributor and distribution tubes.
Must always such valves used in refrigeration evaporators or heat exchangers of large plates, where the pressure drop will be higher than the pressure corresponding to 2 ° C.
The thermostatic expansion valves are developed to regulate the injection of liquid refrigerant to the evaporators. This refrigerant injection is always controlled by a thermostatic element which is located at the top of the expansion valve which is controlled as a function of refrigerant superheat.
A variety of thermostatic expansion valves, eg R-22, R 404-A, R-717 (ammonia). With balanced port, loaded MOP. In all of them the goal is to deliver the maximum efficiency of the evaporator with a suitable overheating.
The first is to analyze and explain the operation of the expansion valve: consists of a separate thermostatic element (1) body by means of a membrane, the thermostatic element is in contact with the bulb (2) through a capillary tube, a body with a seat and orifice (3) and a spring.
Result image for thermostatic expansion valve
Performance
P1: bulb pressure acting on top of the membrane and in the direction of valve opening.
P2: evaporator pressure, which affects the bottom of the membrane and in the direction of valve closing.
P3: the spring force, which affects the bottom of the membrane and the only variable that is controllable by the technician.
When the regulating valve, there is a balance between bulb pressure at the top of the membrane and the pressure against the evaporator and the spring will, this in order to find the most suitable operating overheating.
Overheating
The concept of overheating the heat added is steamed after vaporization in the expansion valve. This can be measured in the place where the bulb is the suction pipe is. The difference between the temperature of the thermometer and the evaporation pressure, translated into temperature that corresponds, the result is overheating in the evaporator, which is designed to operate with a range of warming of 5 ° C. For the Total overheat enough to change the thermometer until the end of the suction pipe 30 centimeters before the compressor, and take the suction pressure to the compressor inlet. The difference in temperature will be the total overheating which must not exceed 15 ° C. It is important to note that these measurements should be made when the temperature has already obtained camera, if for some reason it does not reach the desired temperature It should review the thermal balance or probable clogging by dirt and / or moisture in the cooling system well.
Result image for thermostatic expansion valve
Overheating serves to ensure that liquid refrigerant will be fully evaporated in the evaporator. But there are situations where you need to change the setting of overheating, which can be done when you have distances greater than 15m, in this condition may reduce overheating by turning the screw against clockwise. More than 360 ° in order to look after the compressor is not recommended, remembering that 90% of hermetic compressors cooling is given by the suction gas. On the other hand, if the total is very small overheating will have to raise it and this is achieved by turning the screw for clockwise. It should be noted that the presence or absence of frost ice a suction pipe does not indicate or guarantee the physical state of the refrigerant.
Result image for thermostatic expansion valve
Valves with external pressure equalization
If liquid distributors, expansion valves should always be used with external pressure equalization is used.
The use of liquid distributors generally causes a pressure drop of 14.7 psig in the distributor and distribution tubes.
Must always such valves used in refrigeration evaporators or heat exchangers of large plates, where the pressure drop will be higher than the pressure corresponding to 2 ° C.
Buen post amigo muy completo y entendible
ResponderEliminarGracias espero que te haiga servido
ResponderEliminarSencillamente que es una valvula vet..
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