ALCO EMERSON
Thermostatic expansion valves
Basic data
Working principle
Thermostatic expansion valves ALCO control overheating of refrigerant vapors on output from evaporator. It works as a throttling device between the sides of cooling system with different pressures and ensure that the amount of pumped refrigerant corresponds to the amount of refrigerant evaporated from evaporator. This ensures a full utilization of the evaporator and protects the compressor against suction of wet vapor.
Filling of sensing bulbs
The sensing bulbs are always filled with corresponding mixtures of fillers and their precise amount according to range of valve use.
Liquid charge
Behaviour of valve with liquid charge is influenced solely by temperatures scanned by the sensing bulb and they are exempt from outside influences. The valves react reliably in corresponding time and they stabilize the regulating system. Liquid charge can not be used for MOP function. Maximum temperature of the sensing bulb must not exceed 75°C.
Gas charge
Behaviour of valve with gas charge follows the lowest temperature scanned by the sensing bulb or by a capillary. A failure – overheating, low evaporating temperature – can occur in case that whatever part of the valve is cooler than the sensing bulb. Thermostatic expansion valves ALCO with gas charge enable MOP function and have balanced conditions in the sensing bulb. The balance causes slow opening of the valve, however it causes also its quick closing. The maximum temperature of the sensing bulb is 175°C.
Static overheatingThermostatic expansion valves ALCO are set by producer to optimum overheating. It could be changed only in case of necessity. The setting should be made at the lowest operating evaporating temperature.
Undercooling
Undercooling generally causes higher cooling output. It was included into correction factor K during projection. The correction factor respects the real temperatures of refrigerant at the inlet into the valve. It includes various densities before and after the valve and also different proportion of vapors after expansion. Consistence of wet vapors after throttling depends on operating conditions. High undercooling before the valve causes high volume of liquid component after throttling and increases valve output. The correction factor K does not cover such changes. This can lead to wrong valve assignment. When the undercooling exceeds 15 K, it is necessary further to correct the K factors. Experiences show that too high undercooling can be compensated with additional multiplication by K5 factor.
