Expansion Valve R Series

The R series is the larger thermostatic expansion valve in the range, covering 0.5 to 18 TR (1.76 to 63.4 kW on R22) where the T series runs out of orifice. It is externally equalised throughout, because at these capacities the evaporator almost always has a distributor or a coil pressure drop large enough to upset an internally equalised valve.

Capacity tables are published for R22, R134a, R407C, R404A/R507 and R410A, and selection must be made from the table for the refrigerant actually in the system: the same valve gives noticeably different capacity on R410A than on R22, and a valve sized on the R22 figure will be oversized after a retrofit. The rated evaporating range runs from -40 C to +10 C, so the same body covers freezer, chiller and air-conditioning duties.

Connections are 3/8 inch by 1/2 inch on the smaller sizes and 1/2 inch by 5/8 inch as capacity rises, both with a 1.5 m capillary. Static superheat is adjustable and should be checked after commissioning rather than left at the factory setting, because it interacts with distributor nozzle selection.

Two installation details cause most of the problems at this size. First, the external equaliser must be taken from the suction line downstream of the bulb and should slope back towards the line so oil cannot sit in it and give a false signal. Second, where a distributor is fitted the nozzle has to be matched to the valve capacity - an oversized nozzle starves the circuits and an undersized one floods them, and neither fault looks like a valve problem at first.

For replacement work match both the capacity at the design point and the connection sizes; the physical envelope differs between body sizes.