User Guide

ManualsBrandsSporlan ManualsHVAC SuppliesOVE-15-GA 7/8" x 1-1/8" ODF Thermal Expansion Valve w/ 120" Capillary (15 Ton)

P4 becomes more significant to TEV operation the greater

the port area to effective diaphragm area ratio, and the

greater the pressure drop varies across the valve port.

Balanced Port TEVs

Sporlan introduced the concept of the balanced port thermo-

static expansion valve in 1946 on large tonnage Types T and

W valves. This concept provided the means to either largely

reduce or eliminate the effect of pressure drop across the valve

port. This design utilized a double seating piston operated by

a single pushrod. The two port construction divided the refrig-

erant flow in opposite directions, thereby providing a semi-

balanced pressure differential across the piston.

Improved balanced port designs resulted in a fully balanced

Type O valve, and then the Types (E)BF, SBF, and EBS

valves for smaller capacity applications. For additional infor-

mation on the types and applications of balanced port TEVs,

refer to Page 9, Thermostatic Expansion Valve Applications.

Equalization Method

As previously discussed on Pages 3 and 4, the operation of

the thermostatic expansion valve is determined by the rela-

tionship between three fundamental pressures: bulb pres-

sure, equalizer pressure, and equivalent spring pressure.

These pressures are illustrated in Figure 1. The equalizer

pressure is the evaporator pressure the valve senses. The

means used to transmit this pressure from the refrigeration

system to the underside of the valve diaphragm is referred

to as the equalization method.

Evaporator pressure is transmitted to the underside of

the valve diaphragm by one of two methods. If the valve is

internally equalized, the evaporator pressure at the valve

outlet is transmitted to the diaphragm via a passageway

within the valve body or through a clearance around the

pushrods. If the valve is externally equalized, the under-

side of the valve diaphragm is isolated from the valve outlet

pressure by the use of packing material around the pushrods

or with pushrods which are closely fitted. Evaporator pres-

sure is transmitted to the diaphragm by a tube connecting

the suction line near the evaporator outlet to an external

fitting on the valve. The external fitting is connected to a

passageway which leads to the underside of the valve dia-

phragm. See Figure 2.

Internally equalized TEVs should be limited to single circuit

evaporator coils having a pressure drop no greater than the

equivalent of a 2°F saturated temperature change. Refer to

Table 1 for recommended maximum allowable pressure drop

values for internally equalized valves.

Externally equalized TEVs, however, are not affected by pres-

sure drop across the evaporator, including pressure drop from

refrigerant distributors employed by multi-circuited evaporator

IMPORTANT: The External Equalizer must be used on evaporators which

employ a refrigerant distributor.

coils. An externally equalized TEV may be used for all

refrigeration applications. It provides no operational dis-

advantages with respect to an internally equalized valve

other than requiring an external equalizer line be connected.

Figures 3, 4, and 5 illustrate the effects of evaporator pres-

sure drop on an internally and externally equalized TEV.

When an externally equalized TEV is used, the equalizer

connection on the TEV must be connected to the suction line

near the outlet of the evaporator, and not capped!

Figure 3 shows an internally equalized valve feeding a

single circuit evaporator which has no pressure drop. The

system refrigerant is R-22 and, for the purpose of illustra-

tion, R-22 is also used as the thermostatic charge. The

evaporator pressure at the valve outlet and at the sensing

bulb location is 52 psig. The sum of this pressure and the

12 psi spring pressure produces a 64 psig pressure in the

closing direction. For the valve to properly operate, a 64

psig opening bulb pressure is required to balance pressure.

Since the sensing bulb consists of liquid R-22, its pressure-

temperature characteristic is identical to the saturation

curve of R-22, and a 37°F bulb temperature is required. The

superheat at which the valve is controlling is calculated by

subtracting the saturation temperature of the evaporator

pressure at the sensing bulb location by the bulb tempera-

ture. In this case, the superheat is 9°F.

BULLETIN 10-9 / Page 5

Valve with INTERNAL

Equalizer

Tolerance

Fit

Internal

Equalizer

External

Equalizer

Fitting

Push

Rods

Valve

Outlet

Pressure

Evaporator

Outlet

Pressure

Push

Rods

Valve with EXTERNAL

Equalizer

Figure 2

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04 02 0 – 02 – 04

porDerusserP is— p

431,21 a 00.2 05.1 00.1 57.0

––

22 00.3 00.2 05.1 00.1 75.0

705,205,A404 00.3 05.2 57.1 52.1 00.1

A(717 ainomm ) 00.3 00.2 05.1 00.1

Table 1

37°

Bulb Pressure

64 psig

Evaporator

Inlet Pressure

52 psig

Evaporator

Outlet Pressure

52 psig

Diaphragm

Spring Pressure

12 psi

Closing Pressure............................................................................= 52 + 12 = 64 psig

(Evaporator Inlet Pressure Plus Spring Pressure)

Bulb Pressure Necessary to Open Valve..........................................................64 psig

Bulb Pressure Equivalent to 64 psig.....................................................................37°F

Saturated Temperature Equivalent to Evaporator Outlet Pressure.........................28°F

SUPERHEAT......................................................................................................9°F

Bulb Temperature Minus Saturated Evaporator Temperature

Converted to Temperature = 37°F

Figure 3