Design And Principle Of Operation; Hcd Actuator; Direction Of Action And Fail Position; Hcd Actuator With Hydraulic Circuit - Samson EB 31a-23 Mounting And Operating Instructions

3

Design and principle of operation

3.1 HCD actuator

The HCD actuator is typically used to obtain a decelerated strok-
ing time only at the end of stroke rotation.
The actuators are available in two confi gurations: spring return
and double acting.
Double acting - Type DAP HCD
Refer to Fig. 3-1.
In case of the double acting confi guration air pressure will be
necessary for both strokes
Fig. 3-1: Quarter-turn actuator Type DAP HCD
Spring return - Type SRP HCD
Refer to Fig. 3-2
When air pressure is supplied through port "2" into the actuator
body, the linear force applied on the piston surface generates the
pinion rotation, driving the valve to a defi ned position. At the
same time the actuator springs are compressed.
When air pressure is discharged, the springs are automatically
released, driving the rack and pistons back to the original posi-
tion and thus the valve to the fail-safe position.
Fig. 3-2: Quarter-turn actuator Type SRP HCD
EB 31a-23_EN
Edition: November 2021
Specifi cations subject to change
The actuators can be controlled by different options:
− direct mounting of control devices (for example a solenoid
valve or a manifold) with NAMUR interface,
− threaded connections (to pressurize port "2" and "4") with
air lines from separate electro-pneumatic control system.

3.2 Direction of action and fail position

The standard rotating direction for the HCD actuators is clock-
wise to close.
Standard HCD actuators are designed for 90° rotating angle,
with travel stop allowing adjustment for -5° up to +15° on the
close position and for +5° up to -15° on the open position, see
Fig. 3-3.
Fig. 3-3: Adjustment range
In case of pressure, power or signal failure the springs drive the
actuator in the fail position that can be CCW rotation or CW ro-
tation.
Note
If the actuator is controlled by a control system, the FAIL position
may be different from FAIL OPEN or FAIL CLOSE.
Refer to the actuator model technical data for the FAIL posi-
tion.
For the fail action and direction of rotation available options,
see section "2.1 Actuator name plate".

3.3 HCD actuator with hydraulic circuit

The HCD actuator with hydraulic circuit is typically used to con-
trol the stroking time during all stroke rotation.
If the HCD actuator is equipped with hydraulic circuit, then read
following instruction. The HCD actuator with hydraulic circuit
permits to adjust the actuator opening and closing time operat-
ing the hydraulic valves.
Design and principle of operation
3-1