Siemens POWERS RL 243 MP Technical Instructions

POWERS® Controls

Technical Instructions

Document No. 155-042P25

RL 243-6

September 10, 2018

RL 243 MP Multi-Purpose Relay

Siemens Industry, Inc.

Description

The Powers RL 243 MP Multi-Purpose Relay is a pneumatic auxiliary device designed to
provide a variety of pneumatic control functions for the typical control system.
Applications include direct and reverse acting amplifying, signal advancing, minimum
pressure relay, and lower pressure transfer. (See Figures 2 through 10.)

The relay operates on a force balance principal and is provided with a Powers two-valve
design to assure stability and prevent unnecessary air consumption. Internal relief
assembly prevents signal lock-up and assures fail-safe operation. The relay housing is
provided with integral brackets to facilitate installation without a separate bracket.

A single spring adjustment is provided to allow setting the relay for desired operation.
The relay is adaptable for flush panel mounting to facilitate manual readjustment if
desired.

Product Number

243-0009

Operation

The relay output pressure at port R is dependent upon the adjustable setting of spring
S1, the interaction of pneumatic signals at ports TD and TR, and the availability of a
supply source at port S. The basic relay formula can be expressed as follows:

R = (TD + (S1 - TR) = S

NOTE: (S1 - TR) cannot be less than zero,

Where:

R is the output pressure
TD is a direct acting input variable
S1 is the setting of the adjustment spring
TR is a reverse acting input variable (opposing S1)

Technical Instructions RL 243 MP Multi-Purpose Relay
Document Number 155-042P25
September 10, 2018

Page 2 Siemens Industry, Inc.

Operation,
continued

Figure 1.

The return line pressure R depends on the force exerted by adjustment spring S1 and air
pressures at TD and TR. TR pressure is exerted against the bottom of the upper
diaphragm, opposing S1. However, if S1 is greater than force TR, this difference (S1
minus TR) is transmitted by the stem to the main diaphragm below. The other force
acting downward on the main diaphragm is caused by the air pressure at TD. These
downward forces are balanced by air pressure R pushing up on the main diaphragm.
Spring force S1 is adjustable up to an equivalent pressure of 25 psi.

Specifications

Instrument air supply
Normal 0-2 5 psi (0 to 172 kPa)
Maximum 30 psi (207 kPa)

Temperature limits
Ambient 40 to 120°F (4.4 to 49°C)
Storage -20 to 120°F (-29 to 49°C)

Adjustments Spring S1 0 to 25 psi (0 to 172 kPa)
Hysteresis Within 0.25 psi (1.7 kPa)
Relief valve differential Within 1.0 psi (6.89 kPa)

Accessories
Panel mounting For flush mounting,
with adjustable knob, dial
plate and mounting bracket

Surface bracket For exposed surface mounting
(Use with Panel Mounting Kit above)

RL 243 MP Multi-Purpose Relay Technical Instructions
Document Number 155-042P25
September 10, 2018

Siemens Industry, Inc. Page 3

Application

The multi-purpose relay is factory calibrated with a 15 psi spring adjustment for reverse
acting service. However, the multi-purpose relay provides a number of specific control
actions which are frequently utilized in control systems. Some of the typical applications
where this relay can be applied are as follows. Additional applications can be obtained
depending upon how it is piped and applied with other devices in a single system.

• Direct acting amplifying (See Figure 2).

• Reverse acting amplifying (See Figure 3).

• Lower pressure transfer relay (See Figure 4).

• Signal advancing relay (See Figure 5).

• Minimum pressure relay (See Figure 6).

• DA or RA limit control (See Figures 7 and 8).

• Signal inverting relay (See Figure 9).

• Characterized minimum pressure relay (See Figure 10).

Direct Acting (DA)
Amplifying Relay

Output pressure will vary directly with input pressure. Relay is fail-safe and cannot
generate an output signal unless a source of air is available at S-port (Figure 2).

Figure 2. Direct Acting (DA) Amplifying Relay.