OPERATING MANUAL
Pneumatic rotary drive units type ST | DT
Wesa-Armaturen GmbH
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+49 (0)7181-404-0
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Operating manual
D-73650 Winterbach
Drive units ST | DT
Date of issue 10-2019
3.0. Function characteristics
The pneumatic servo drive units have the function characteristics shown in Figures 1A-1B-1C-1D / 1E-1F-
1G-1H. Compressed air connection A (2) is connected with the hollow chamber between the pistons and
compressed air connection B (4) is connected with the external hollow chambers between the pistons
and the side covers. The servo drive units are supplied as standard with an octagon socket on the output
side in which either an octagonal shaft or a square shaft can be fitted in any configuration (45° or 90°).
To order the servo drive units can also be supplied with the output versions listed below.
The compressed air connection can be made direct at the compressed air connections or through control
valves with a NAMUR connection.
Double-action servo drive units
(without reset springs)
If compressed air is supplied to compressed air connection A (2), the pistons move outwards as far as
possible up to the stroke limiting pin and the drive pinion moves in a 90° swing movement. When
compressed air is supplied to connection B (4), the outer chambers of the drive housing are filled with
compressed air and the pistons returned to their initial positions. The drive pinion returns to its original
position through a 90° swing movement.
Single-action servo drive units
( with reset springs)
If compressed air is supplied to compressed air connection A (2), the pistons move outwards as far as
possible up to the stroke limiting pin which tensions the reset springs. When the compressed air supply
at compressed air connection A (2) is switched off, the pistons are pushed back to their original positions
by the tensioned springs. If the servo drive units also have a stroke limit for the inner position of the
pistons (initial position), they move back to the initial position as far as possible up to that limit.
4.0. Installation
Important safety information
During installation, the drive unit must be depressurised for safety reasons. When connecting the air to
the drive unit, ensure extreme cleanliness, with the thread connections, screw connections and seals, in
particular, being clean and dirt-free. If you install accessories on the drive unit, ensure that the top end
of the shaft remains clear so that if it needs to be controlled manually at a later date, this is possible.
Before you install the drive unit on a fitting, ensure that the fitting is in the correct initial position
depending on the required direction of rotation.
The servo drives are designed to ensure easy, straightforward installation. They have ISO 511 (DIN 333/9)
interfaces to connect fittings, signal units and control units. If the appropriate fittings are used, they are
suitable for direct installation and also for installation on fittings with a shaft adapter and installation
bridge.
