Emerson 122A Data Sheet

Bulletin 71.7:122A

Type 122A Three-Way Switching Valve

Introduction

The Type 122A valve (see Figure 1) is a high­capacity, economical three-way pneumatic switching
valve for on-off applications. This valve can be
used for diverging or converging gaseous service,
diverging liquid service with gas-loaded liquids, and
converging liquid service. Six spring ranges are
available for control pressures from 3 to 150 psig
(0,21 to 10,3 bar).

Features

• Convenient Installation—Compact construction

permits easy handling and installation.

December 2009

• Easy Leak Detection—Vent hole between body
and actuator stem seals allows rapid detection of
body or actuator leakage.

• Easy Maintenance—With the bottom piping
disconnected, the valve can be completely
disassembled without removing it from the line.

Principle of Operation

Refer to Figure 2. The ow through the Type 122A

valve is normally from port A to C, with the spring
force holding the valve plug down on port B
(diverging service).

As the pressure under the diaphragm is increased
through port D, it acts against the force of the spring.
When the control pressure overcomes the force of
the spring, the valve begins to stroke, opening port B.
Once the pressure under the diaphragm reaches
setpoint plus build-up, the valve completes its stroke
and the port C seat ring is closed. The valve will only
fully stroke when build-up above setpoint is achieved.

The point at which the valve completes its stroke
and the pressure change necessary to do this
are dependent on the spring rate and the setpoint
chosen. The set pressure is easily changed by
adjusting the screw at the top of the valve.

W3141-1*

Figure 1. Type 122A Three-Way Switching Valve

Installation

The Type 122A valve may be installed in any position.
Be certain the spring case vent opening is pointing
down and is protected against the entrance of the
moisture and any other material that may plug the
vent. The Type 122A valve should not be used in
installations where water hammer can be experienced.
Dimensions are shown in Figure 3.

Overpressure Protection

Type 122A Three-Way Switching Valves have
maximum outlet pressure ratings that are lower than
their maximum inlet pressure ratings. A pressure­relieving or pressure-limiting device is needed if inlet
pressure can exceed the maximum outlet pressure
rating. Overpressuring any portion of a switching
valve or associated equipment may cause leakage,

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D200075X012

Bulletin 71.7:122A

INLET PRESSURE
OUTLET PRESSURE
ATMOSPHERIC PRESSURE

Specications

Body Sizes and End Connection Styles

Connections A and C: Available in 3/4 or 1 body
sizes with NPT end connections
Connection B: 3/4 NPT

Maximum Inlet Pressure

(1)

150 psig (10,3 bar)

Set Pressure Ranges

See Table 1

Maximum Control Pressure to Diaphragm

(1)

150 psig (10,3 bar)

Temperature Capabilities

(1)

-20° to 150°F (-29° to 66°C)

Construction Materials

Valve Body: Cast iron
Bottom Connector: Steel
Spring Case: Aluminum
Lower Diaphragm Case: Cast iron
Disk and Disk Holder Assembly: Nitrile (NBR)
and Aluminum or Nitrile (NBR) and Stainless steel

1. The pressure/temperature limits in this Bulletin and any applicable standard or code limitation should not be exceeded.

2. At an inlet pressure of 25 psig (1,7 bar) and with full pressure drop across the body.

Orice: Aluminum or Stainless steel
Diaphragm: Neoprene (CR)
Gaskets: Composition
O-Rings: Nitrile (NBR)
Washers: Zinc-plated steel and
302 Stainless steel
Spring: Zinc-plated steel

Flow Coefcients

(2)

C

g

Connection A to B: 138
Connection A to C: 131
C

1

Connection A to B: 28.0
Connection A to C: 32.5

Control Connection

1/4 NPT internal

Vent Connection

1/4 NPT internal with screen

Approximate Weight

5 pounds (2 kg)

W0157

INLET PRESSURE
OUTLET PRESSURE

ATMOSPHERIC PRESSURE

STEM

PORT D

PORT A

PORT B

ADJUSTING SCREW

SPRING

DIAPHRAGM

UPPER VAVE SEAT

PORT C

VALVE

LOWER VAVE SEAT

Figure 2. Type 122A Three-Way Switching Valve Operational Schematic

2