Question

Question 4 A refrigeration system operating on R22, experiences liquid knock during start-up. You suspect that one of the causes could be that the wrong expansion valve was selected/ The following information is available (a) Refrigeration capacity: 80 kVw (b) Suction pressure measured at compressor: 350 kPa (abs) (c) Condensing pressure : 1600 kPa (d) Temperature of liquid leaving condenser : 40°C (e) Neglect pressure drop in condenser and evaporator (f) Pressure drop across distributor and evaporator 170 kPa (g) Pressure drop in suction line 1,6 K equivalent (h) Pressure drop in liquid line : 0,5 K equivalent (i) Pressure drop in solenoid valve and drier/filter in liquid line :35 kPa Would you say that the Danfoss Type TEX 20-30 thermostatic expansion valve that is installed in the system is correctly sized ? If so, motivate. If not, what would be your selectiorn

Answer 1

Abnormal noise from compressor are due to folllowing reasons ,

Causes

1. Compressor capacity too high during start-up
2. Oil pressure too low
3. Liquid refrigerant in suction line
4. Incorrect alignment of motor and compressor. Loose bolts in coupling
5. Worn or defective bearings
6. Too much oil circulating through the plant, resulting in too low oil level in compressor
7. Capacity regulation oscillating owing to failing oil pressure    Based on above information the knocking when staring is not related with thermostatic expansion valve and its correctly sized. knocking is due to high compressor capcity when the time of starting . you can proceed with danfoss type TEX 20-30 THERMOSTATIC EXPANSION VALVE