How do txv work

When a valve is overfeeding the first thing to check is bulb insulation, placement, and strapping. This happens because techs will find a system with low suction pressure and assume that means it is low on refrigerant. They will then start to add refrigerant and the TXV will respond by closing further the more refrigerant is added.

This occurs because the tech is paying too much attention to suction pressure without considering the other readings. First take all of your refrigerant readings as well as your liquid line and suction temperature at both ends on a split system. This means superheat, subcooling, suction saturation evaporator coil temp , and liquid saturation condensing temp.

In refrigeration, we do this same thing by looking for a clear sight glass. The next thing that a TXV needs is enough liquid pressure to have the required pressure differential.

This amount of required pressure differential will vary a bit based on the valve but usually, we want to see a PSI minimum difference between the liquid line pressure and the desired evaporator pressure. If the head pressure drops too low due to low ambient conditions this can come into play and impact the ability of the valve to do its job.

Once this is all confirmed then it is simply a matter of checking the superheat at the end of the evaporator. Keep in mind that some valves will have a screen right before the valve and this can be the cause of the restriction rather than the valve. When you find the point of temperature you find the point of pressure drop, just remember that the TXV is designed to provide pressure to maintain a fairly fixed superheat.

The ballast dampens the rate of expansion within the bulb, stabilizing the bulb pressure against the diaphragm by dampening the rate of temperature change to the bulb charge compared to the rate of temperature change of the suction line. This stabilization ensures that the TXV operates more efficiently and better protects the compressor.

There are two common approaches to what makes up bulb charge fluid. The first approach is to use the same refrigerant that is used in the system, i. The other common approach—and the one that Danfoss recommends—is called a cross charge. Cross charged bulbs mix a combination of different refrigerants with gases to flatten the pressure-temperature P-T curve see Figure 8. Cross charges enable the TXV to perform similarly regarding the change in opening degree for a given change in superheat across a range of evaporator temperatures.

Go to thermostatic expansion valves. Home page Service and support Case stories How thermostatic expansion valves work. How thermostatic expansion valves work. TXV parts. TXV operation. Internal versus external equalization.

Our product reviews and recommendations are researched and backed by real buyers and industry experts, not dictated by our partners. One of the most important components of an air conditioner may be the thermostatic expansion valve, also known as the TXV. A TXV is essentially a meter. This change causes the refrigerant to boil and change from liquid form to a vapor. The thermostatic expansion valve measures the superheat from the liquid refrigerant being boiled off in order to maintain a constant temperature.

Depending on the heat reading, the AC expansion valve will increase or decrease how much refrigerant flows to the evaporator. Thermostatic expansion valves come in two types: externally- or internally-equalized.

A thermal expansion valve keeps the system running as efficiently as possible while protecting the AC compressor from damage that could be caused by liquid refrigerant. Thermal expansion valves work under extremely high pressure and temperatures which tend to fluctuate up and down.