EP0150042A2 - Power device for command and regulation apparatuses - Google Patents

Abstract

1. Apparatus for driving control and regulating means which possesses a piston (1) which can move in a working cylinder (3) and both of whose end faces (2) can be brought into contact with a pneumatic or hydraulic medium, and in which the piston (1) can be additionally actuated by means of a reset rod (4) which can be inserted into the working cylinder (3) from outside, the reset rod (4) being connected to an actuating member (5) which separates a chamber (6), with a feed line (7) for a pneumatic or hydraulic medium, from a second chamber (8) which has a venting or air inlet port (9) and contains one or more springs (10) which hold the actuating member (5) under tension, wherein the actuating member consists of a membrane (5) connected to a spring plate (14), and a stop (4a) for limiting the initial spring bias is provided.

Description

The present invention relates to a device for driving open-loop or closed-loop control devices with a piston movably arranged in a working cylinder, the piston surfaces of which can be acted upon pneumatically or hydraulically on both sides, and in which the piston can also be actuated by a reset rod that can be inserted into the working cylinder from the outside.

In the chemical industry, diaphragm or piston drives are preferred for control and regulation.

In order to be able to move to and hold the safety position in the event of an auxiliary power failure, these drives are provided with a spring return or connected to a pressurized buffer volume ("air" spring). In the case of actuators with spring return, the spring must also be moved with every stroke or rotary movement.

With the "air" spring, the pressure in the buffer volume must always be present. Automatic monitoring is required to ensure this.

It was therefore the object of the invention to develop a drive which meets the high safety requirements of chemical process engineering reliably and inexpensively, and in which the spring installed for safety reasons is only effective in the event of a fault.

This object is achieved according to the invention in a device of the type mentioned at the outset in that the reset rod is connected to a membrane which separates a space with a feed for a pneumatic or hydraulic medium from a second space with a ventilation opening in which one or more springs are arranged to hold the membrane under tension.

• 1. Im Normalbetrieb - bei vorhandenem Steuermedium - arbeitet der Antrieb ohne Federrückstellung als doppelt-wirkender Antrieb: Spr/P
  • - somit liefert dieser Antrieb ein wesentlich höheres Drehmoment als ein Antrieb mit Federrückstellung bei vergleichbarem Kolbendurchmesser;
  • - das abgegebene Drehmoment ist konstant und belastet die Armaturenspindel weniger;
  • - bei vergleichbaren Drehmomenten hat der neue Antrieb ein geringeres Gewicht;
  • - der Luftverbrauch ist ebenfalls geringer;
  • - das Drehmoment ist sehr leicht durch den Steuerdruck veränderbar.
• 2. Bei Ausfall der Hilfsenergie oder bei einer defekten Membrane arbeitet der Antrieb einfach wirkend - also mit Federrückstellung.
  Nur in diesen Fällen wird die Kompensation der Federkraft aufgehoben.
  • - Somit werden die Federn nur ganz selten betätigt;
  • - durch die geringe Wechselbeanspruchung der Feder(n) wird ihre Lebensdauer vergrößert;
  • - die Verfügbarkeit des Antriebes ist sehr groß, da die Abdichtung durch eine Membrane außerordentlich zuverlässig ist.
  • - Auch nach einer längeren Verweilzeit in der Endstellung mit komprimierten Federn ist kein Blockieren der Rückstellstange zu befürchten, da die Membrane ohne Reibungsverluste bewegt wird.

The advantage of the device according to the invention lies in different modes of operation:

• 1. In normal operation - with existing control medium - the actuator works without spring return as a double-acting actuator: Spr / P
  • - Thus, this drive delivers a much higher torque than a drive with spring return with a comparable piston diameter;
  • - The torque output is constant and puts less strain on the valve stem;
  • - At comparable torques, the new drive has a lower weight;
  • - Air consumption is also lower;
  • - The torque can be changed very easily by the control pressure.
• 2. If the power supply fails or the diaphragm is defective, the actuator works in a single-acting manner - ie with spring return.
  Only in these cases is the compensation of the spring force canceled.
  • - Thus the springs are only used very rarely;
  • - The low alternating stress on the spring (s) increases their lifespan;
  • - The availability of the drive is very large because the sealing by a membrane is extremely reliable.
  • - Even after a longer dwell in the end position with compressed springs, there is no fear of the reset rod blocking, since the diaphragm is moved without loss of friction.

A possible embodiment of the device according to the invention is shown schematically in the drawing and is explained in more detail below: Instead of a piston drive with a laser reset, a double-acting piston drive 1 is used according to the invention in a working chamber 3 with an attached or integrated spring return unit; in the case of the double-acting piston drive, the housing cover in which the spring would sit is provided with a bushing 11 including bearing 12 and seal 13 for a reset rod 4.

The reset rod 4 is firmly connected to a unit consisting of a membrane 5, spring (spring assembly) 10 and spring plate 14. The membrane 5 separates a space 6 with a feed 7 for a pneumatic or hydraulic medium from a second space 8 with a ventilation or ventilation opening 9, in which the spring (s) 10 are arranged.

When the pressure of the control medium (gas or liquid) is sufficiently high, the spring (s) 10 is (are) compressed via the diaphragm 5 and thus the reset rod 4 is held at the end of the working chamber 15.

The double-acting piston 1 can thus be moved into all desired positions by the control medium acting on the piston surfaces 2 and a control or regulating unit 16 with the feeds 7, 17, 18.

If the control medium fails, the reset rod 4 is moved into the working chamber 15 by the spring (s) 10. The piston 1 is pressed into the safety position and held by the reset rod 4 and the spring (s) 10.

The stroke of the spring (s) 10 and the diaphragm 5 must be coordinated with the stroke of the piston 1. This results in a restriction of the stroke when using the membrane 5.

The size of the spring force must either be adapted to the force of the piston 1 or the desired restoring force. The membrane area is chosen so large that the control medium holds the reset rod 4 outside the adjustment range of the piston 1 at the existing pressure.

Claims (1)

Device for driving open-loop or closed-loop control devices with a piston (1) movably arranged in a working cylinder (3), the piston surfaces (2) of which can be acted upon pneumatically or hydraulically on both sides, and in which the piston (1) is moved from the outside into the working cylinder (3) insertable resetting bar (4) is additionally actuated, characterized ekennzeichnet ^q, that is, the return rod ₍₄₎ connected to a diaphragm (5) having a space (6) with a feed (7) for a pneumatic or hydraulic medium separates from a second space (8) with a ventilation opening (9) in which one or more springs (10) are arranged which hold the diaphragm (5) under prestress.

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