The different types of expanslon v/v and explain which type of expansion v/v do
you have onboard
Ans - There are basically four types of valves that are in used. These valves are also refer to as metering devices.
Automatic Exp. Valves
Thermostatic Exp. Valves
Capillary Tubes
Float Valves
Automatic Expansion Valve regulates the flow of refrigerant from the liquid line to the evaporator
by using a pressure-actuated diaphragm. It maintains a constant pressure in the evaporator.
The setback is that it is not efficient if the load fluctuates hence this type is not suitable for use in air
conditioning as the load fluctuates a lot during its operation.
Thermostatic Expansion Valve uses a valve mechanism to control the flow of liquid refrigerant intothe evaporator coil.
The flow is controlled by the pressure in the evaporator.
This type of metering device is able to operate well when the load fluctuates and hence is suitable
for use in air conditioning system. When the evaporator warms, the valve provides a higher flow rate
and when it cools, it reduces the flow rate.
It is also commonly refer to as TXV, TEV or TX valve. There is a sensing bulb which detects the
temperature of the coil and is usually located at a higher temperature within the evaporator.
The bulb must be clamped firmly to the coil to ensure proper sensing. When the temperature of the
evaporator increases due to the demand for cooling, the pressure in 'the bulb will also increase
hence pushing the spring to open the valve.
Similarly, when the temperature of the evaporator reduces due to a lack of demand for cooling, the
pressure in the bulb will drop hence causing the spring to close the valve.
Capillary Tube is a tube with small internal diameter and could be coiled for part of its length.
It isinstalled to the suction line. A filter-drier is sometimes fitted before the tube to remove dirt or moisture from the refrigerant..
This device is simple, does not have any moving part and lasts longer. In order to use this device, the
amount of refrigerant in the system must be properly calibrated at factory level.
Due to its lower cost compared to TXV, this metering device is used in units that are produced in
large quantity such as room or window air conditioners.
Depending on the capacity design of the system, the capillary tube internal diameter that is commonly used range from 0.031" to 0.065" and the outer diameter from 0.083" to 0.130".
Float Valve is actuated by a float that is immersed in the liquid refrigerant. Both low-side float and high side-float are used to control the flow of liquid refrigerant.
The low-side float helps to maintain a constant level of liquid refrigerant in the evaporator. It opens when there Is no liquid in the evap. and closes when there is liquid in the evap.
The high-side float is located at the high pressure side of the system and maintain a constant level of refrigerant in the condenser. When the compressor operates, the condensed refrigerant flows to the
float chamber and opens the valve.
This causes the refrigerant to flow into the evaporator where it is stored . As the liquid level falls in the float chamber ,the valve opening will close hence preventing the liquid from flowing to the evaporator.
Now,
Most of the ship have thermostatic expansion valve so I try to tell you the each and every point with
regard to the thermostatic expansion v/v
1. TEV Is fitted in between the solenoid and evaporator
10 % liquld flash off and convert Into the gas and this gas absorbs the latent heat of
remaining liquid refrigerant, so due to this temperature of the refrigerant drops
3. Flash off usually occur in the TEV because of the throttling effect
4. So, 90 % of the liquid go into the evaporator and start boiling inside the evaporator coil
because it take heat from the surrounding (Meat, Fish and Vegetable room).
5. How much degree of superheat we need to maintaln at the outlet of evaporator that is been
decided by the TEV
6. If too much flashing occur in TEV then whole of your liquid convert to gas in the expanslon
v/v itself and no cooling effect in the evaporator
7. To reduce too much flashing, we give subcoollng in the condenser but little flashing is
required to reduce the temperature
Note - 1.ln cold countries it is difficult to achleve the temperature because too much subcooling is
provided In the condenser because during cold weather outside sea temperature drops to 10 degree
centigrade so because of excess subcooling no flash up will be there in the expansion v/v anc
without flash up It is difficult to reduce the refrigerant temperature
2.5ensing bulb of the TEV contains the same refrigerant that what we use in the system
Important polnts to note from the dlagram -
Valveiwill remain open, if P1> P2+ P3
P1 = Pressure act on the upward side of the diaphgram because of the sensing bulb
P2 = Spring Pressure
P3 = Pressure act from the downward side because of the liquid refrigerant
you have onboard
Ans - There are basically four types of valves that are in used. These valves are also refer to as metering devices.
Automatic Exp. Valves
Thermostatic Exp. Valves
Capillary Tubes
Float Valves
Automatic Expansion Valve regulates the flow of refrigerant from the liquid line to the evaporator
by using a pressure-actuated diaphragm. It maintains a constant pressure in the evaporator.
The setback is that it is not efficient if the load fluctuates hence this type is not suitable for use in air
conditioning as the load fluctuates a lot during its operation.
Thermostatic Expansion Valve uses a valve mechanism to control the flow of liquid refrigerant intothe evaporator coil.
The flow is controlled by the pressure in the evaporator.
This type of metering device is able to operate well when the load fluctuates and hence is suitable
for use in air conditioning system. When the evaporator warms, the valve provides a higher flow rate
and when it cools, it reduces the flow rate.
It is also commonly refer to as TXV, TEV or TX valve. There is a sensing bulb which detects the
temperature of the coil and is usually located at a higher temperature within the evaporator.
The bulb must be clamped firmly to the coil to ensure proper sensing. When the temperature of the
evaporator increases due to the demand for cooling, the pressure in 'the bulb will also increase
hence pushing the spring to open the valve.
Similarly, when the temperature of the evaporator reduces due to a lack of demand for cooling, the
pressure in the bulb will drop hence causing the spring to close the valve.
Capillary Tube is a tube with small internal diameter and could be coiled for part of its length.
It isinstalled to the suction line. A filter-drier is sometimes fitted before the tube to remove dirt or moisture from the refrigerant..
This device is simple, does not have any moving part and lasts longer. In order to use this device, the
amount of refrigerant in the system must be properly calibrated at factory level.
Due to its lower cost compared to TXV, this metering device is used in units that are produced in
large quantity such as room or window air conditioners.
Depending on the capacity design of the system, the capillary tube internal diameter that is commonly used range from 0.031" to 0.065" and the outer diameter from 0.083" to 0.130".
Float Valve is actuated by a float that is immersed in the liquid refrigerant. Both low-side float and high side-float are used to control the flow of liquid refrigerant.
The low-side float helps to maintain a constant level of liquid refrigerant in the evaporator. It opens when there Is no liquid in the evap. and closes when there is liquid in the evap.
The high-side float is located at the high pressure side of the system and maintain a constant level of refrigerant in the condenser. When the compressor operates, the condensed refrigerant flows to the
float chamber and opens the valve.
This causes the refrigerant to flow into the evaporator where it is stored . As the liquid level falls in the float chamber ,the valve opening will close hence preventing the liquid from flowing to the evaporator.
Now,
Most of the ship have thermostatic expansion valve so I try to tell you the each and every point with
regard to the thermostatic expansion v/v
1. TEV Is fitted in between the solenoid and evaporator
10 % liquld flash off and convert Into the gas and this gas absorbs the latent heat of
remaining liquid refrigerant, so due to this temperature of the refrigerant drops
3. Flash off usually occur in the TEV because of the throttling effect
4. So, 90 % of the liquid go into the evaporator and start boiling inside the evaporator coil
because it take heat from the surrounding (Meat, Fish and Vegetable room).
5. How much degree of superheat we need to maintaln at the outlet of evaporator that is been
decided by the TEV
6. If too much flashing occur in TEV then whole of your liquid convert to gas in the expanslon
v/v itself and no cooling effect in the evaporator
7. To reduce too much flashing, we give subcoollng in the condenser but little flashing is
required to reduce the temperature
Note - 1.ln cold countries it is difficult to achleve the temperature because too much subcooling is
provided In the condenser because during cold weather outside sea temperature drops to 10 degree
centigrade so because of excess subcooling no flash up will be there in the expansion v/v anc
without flash up It is difficult to reduce the refrigerant temperature
2.5ensing bulb of the TEV contains the same refrigerant that what we use in the system
Important polnts to note from the dlagram -
Valveiwill remain open, if P1> P2+ P3
P1 = Pressure act on the upward side of the diaphgram because of the sensing bulb
P2 = Spring Pressure
P3 = Pressure act from the downward side because of the liquid refrigerant
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