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Technical Instructions POWERS™ Controls No. 4 Pneumatic Damper Actuator

Document Number 155-032P25

October 10, 2005

Page 6 Siemens Building Technologies, Inc.

Operation

Standard Actuator

(Figure 3)

The air tubing from a controlling instrument connects to the actuator's upper housing.

With no control pressure to the actuator, the compression spring forces the diaphragm

and actuator shaft toward the upper housing, but is limited by the jam nut on the

actuator shaft. As the control pressure on the diaphragm increases, the spring

compression is overcome and the actuator shaft gradually moves outward. Conversely,

as control pressure decreases, the spring returns the shaft to the position at which the

air pressure on the diaphragm balances the spring tension. For each value of control

pressure there is a corresponding position of the shaft.

Hesitation Actuator

(Figure 4)

The branch or return pressure from the controlling instrument connects to the upper

housing of the actuator. With no branch pressure to the motor, the main spring forces

the actuator shaft toward the upper housing, but is limited by the jam nut on the actuator

shaft. As the branch pressure on the diaphragm increases from 0 to 2 psi (0 to 14 kPa),

the compressive force in the main spring prevents the actuator shaft from moving. As

the branch pressure increases from 2 to 3 psi (14 to 21 kPa), the force in the main

spring is overcome and the actuator shaft moves to its hesitation point. At the hesitation

point, the main spring seat is in contact with the retard spring seat. The compressive

force in the retard spring prevents further actuator shaft travel between 3 and 8 psi (21

and 55 kPa). Above 8 psi (55 kPa), the resisting force in the retard spring is overcome

and the actuator shaft moves to its maximum stroke between 8 and 13 psi (55 and 90

a).

Table 3. Construction Components (Figures 3 and 4).

Item Part No. Material Description Item Part No. Material Description

1 333-099 Aluminum Upper housing with pivot ears 7 331-915 Music wire Retainer clip

2 333-071 EPDM Diaphragm (Package of 5) 8 — Stl. tubing Spring guide

3 — Steel Lower housing 9 — Music wire Hesitation spring

4 — Oil-tempered steel Spring 10 — Steel Cycle adjusting rod

5 — Zytel Bearing plate 11 041-100 Brass 10-32 Hex nut

6 — — Piston cup/stem

Figure 3. Standard Actuator.

Figure 4. Hesitation Actuator.

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