US3757646A

US3757646A - Safety circuit for a working cylinder

Info

Publication number: US3757646A
Application number: US00142192A
Authority: US
Inventors: R Rohner
Original assignee: Sulzer AG
Current assignee: Sulzer AG
Priority date: 1970-05-21
Filing date: 1971-05-11
Publication date: 1973-09-11
Anticipated expiration: 1990-09-11
Also published as: FR2090187A1; FR2090187B1; BE767456A; FI57172C; FI57172B; CA930283A; GB1306786A

Abstract

Upon reception of a safety signal, the power amplifier in the form of a control valve communicates the pressure fluid duct with the non-return valve piston to open the non-return valve. This allows a flow between the upper working cylinder chamber and the lower cylinder chamber so that the piston is moved into a safety position. Should the pressure in the fluid duct be insufficient, the power amplifier is switched into communication with the upper working cylinder to cause the non-return valve to open. This also allows a flow between the two cylinder chambers.

Description

[ Sept. 11, 1973 [54] SAFETY CIRCUIT FOR A WORKING 2,427,549 9/1947 Carlson 91/437 X CYLINDER 2,855,900 10/1958 Elmer 3,604,313 9/1971 Fruehauf 91/438 Inventor: Rudolf Rohnelr. Wmterthur. 3,608,431 9/1971 Pease 91/437 Switzerland [73] Assignee: Sul zer Brothers Ltd., Winterthur, primary Examinervlrwin Cohen Swltzerland Attorney-Kenyon & Kenyon Reilly Carr & Chapin [22] Filed: May 11, 1971 [30] Foreign Application Priority Data Upon reception of a safety signal, the power amplifier M 21 1970 Switzerland 7514/70 1n the form of a control valve communicates the presay 6 1 S l d 101 1 sure fluid duct with the non-return valve piston to open wltzer an ,7 the non-return valve. This allows a flow between the upper working cylinder chamber and the lower cyling der chamber so that the piston is moved into a safety [58] 1 91/539 438 437' position. Should the pressure in the fluid duct be insufe 0 mm 1 3 ficient, the power amplifier is switched into communication with the upper working cylinder to cause the non-return valve to open. This also allows a flow be- [56] uNlTEif g g xg gs ggrENTs tween the two cylinder chambers.

2,352,334 6/1944 Macomber ..l 92/131 3 Claims, 2 Drawing Figures I Z3 .1 .1 30 1 12 1 $2 2 l 1 1 32b 34 ll, 33 54 35 35 33 19 1.1:! 3 -1 34b 23 i 31 PATENTEDSEH 1 I915 375?. 646

' sum 2 OF 2 SAFETY CIRCUTT FOR A WORKING CYLTNDER This invention relates to a safety circuit and, more particularly, to a safety circuit for a hydraulic or pneumatic valve installation.

Heretofore, safety circuits with a hydraulic or pneumatic working cylinder, for example, for controlling a valve, have been known to have a double acting piston in the cylinder which is adapted to traverse into a safety position due to the action of an energy source in the event of a pressure drop of the medium in the working cylinder. Generally, these working cylinders have had cylinder chambers which are separated by the piston and which communicate with each other through valve means which are biased by a safety signal. In some instances, a safety circuit of this kind has been proposed for a by-pass valve disposed on a live steam line. Also, in order to minimize the losses of hydraulic medium, it has been necessary for the valve means to be constructed with small clearances. Practical operation, however, has shown that if such a valve means has not been operated for a prolonged period of time, the valve means may become blocked by resinous matter, for example, due to gumming of the hydraulic medium, so that a substantial force is required to actuate the valve means. if this occurs, the means for controlling the valve means such as an electro-magnet which supplies the force, is then unable to ensure reliable functioning of the safety circuit.

Accordingly, it is an object of the invention to provide a safety circuit which is actuated with a degree of probability bordering on reliability, as soon as a safety signal appears.

It is another object of the invention to provide for the operation of a servomotor for a valve despite jamming of any valve parts due to a resinous accumulation.

Briefly, the invention. provides a servomotor for operating a valve with a safety circuit which is able to actuate the servomotor to move a piston thereof into a safety position. The valve may, for example, be a bypass valve in a vapor generating plant while the servomotor utilizes an energy source to initiate movement of a piston. This energy source may be represented by the pressure of the flow medium which acts on the valve body of the valve or by a spring disposed in the working cylinder.

In one embodiment, the servomotor has a piston therein which divides a working cylinder of the servomotor into two chambers while the safety circuit includes a valve means which is connected to the cylinder chambers for moving the piston in response to a safety signal and a power amplifier which isdisposed in the path of the safety signal. In addition, the power amplifier is connected via an automatic selector circuit to a source of pressure medium for the servomotor and to the working cylinder side which corresponds to the safety position of the piston. The selector circuit advantageously comprises two non-return valves whose operating directions are in opposition to each other.

The power amplifier ensures actuation of the valve means even if the valve means has become jammed by resinous matter after prolonged idleness. Also, if the pressure of the medium diminishes or drops below a certain value at the moment at which a safety signal appears, and if the piston nevertheless does not traverse .into the safety position, the selector circuit will come into action and ensure that the piston nevertheless traverses into the safety position.

ln another embodiment, a non-return valve is disposed between the valve means and the cylinder chamber. disposed opposite to the cylinder chamber corresponding to,the safety position of the piston. This non' return valve is constructed. to permit flow only from cylinder chamber to cylinder chamber and the actuation of the valve means is performed from that flow side of the valve means which is disposed between the valve means and the non-return valve. The advantage of this is that in normal operation, that is, when the valve means is closed, the line section disposed between the valve means and the non-return valve is not provided with any pressure medium so that no leakage losses can occur in the valve means.

The power amplifier can be constructed with a multiple piston or as a simple change-over element. In the case where the power amplifier is constructed as a change-over element the amplifier comprises a control valve with a single-acting piston. The advantage of this latter construction is that the power amplifier has only a single piston clearance at which the pressure medium may escape to the relief side. This advantage becomes effective if the medium, controlled by the abovementioned valve, is used as the pressure medium in the safety circuit.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a safety circuit according to the invention connected to a servomotor for a valve; and

FIG. 2 illustrates a modified safety circuit according to the invention.

Referring to FIG. l, a servomotor 1 includes a hydraulic (or pneumatic) working cylinder 2 and a double-acting piston 3 which is slidably mounted in the working cylinder 2 to divide the cylinder 2 into two chambers 2a, 2b. The piston 3 also carries a piston rod 4 which connects to a valve body 5 of a valve 6 such that the servomotor l is adapted to drive the valve body 5. The valve 6 controls the transfer of a flow medium from a chamber or inlet port 6a to a chamber or outlet port 6b. The working cylinder 2 of the servomotor l is also provided with an energy accumulator 110 in the form of a spring 10 which acts on the piston 3 so that the valve 6 opens when the pressure of a control fluid in the cylinder chamber 2a of the working cylinder 2 diminishes or drops below a defined value, and is retained in an open state, independently of any static or dynamic forces of the flow medium controlled by the valve 6 acting on the valve body 5. Instead of being represented by a spring, the energy source may also be represented by the pressure of the flow medium which acts on the valve body 5 coupled to the valve rod 4.

In normal operation of the system to be protected, the servomotor 1 is controlled by a control valve 13 through ducts ill, 12 which are connected to the chambers 2a, 2b. The control valve 13 includes a control piston 15 which bears on a spring 116 and a signal line 18, through which control signals reach the control valve 13 is connected to the valve 13. Furthermore, the control valve T3 is provided with a port 19 which communicates through a pressure fluid duct 20 to a pressure fluid pump 21 while a pair of

other ports

22, 23 of the control valve 13 are connected to an oil sump through a discharge duct 24 for the control fluid. When disposed in a suitable position, the control piston l3 connects the cylinder chamber 2a through the duct 11 with the pressure fluid duct and connects the cylinder chamber 2b with the discharge duct 24 so that the piston is moved in the direction of the cylinder chamber 2b under the influence of the control fluid.

A safety circuit is connected to the servomotor 1 and includes

ducts

30, 31 which are respectively connected to the cylinder chambers 2a, 2b on both sides of the piston 3 of the servomotor 1. In addition, a pair of

nonreturn valves

32, 33 are disposed between the

ducts

30, 31 with the valve body 32a of the non-return valve 32 being biased by a spring 321) while the valve body 330 of the non-return valve 33 is connected to a piston 34 which is adapted to move axially in a housing 35. The non-return valve 33 is also associated with a hydraulic or pneumatic power amplifier which takes the form of a control valve 40. The control valve 40, in turn, is controlled by an electro-magnet 41 with a plunger armature 41a which is coupled to a control piston 40a in the control valve 40. The control valve 40 is constructed to have a substantial amount of clearance so that it can be easily operated by the electro-mag'net 41. A fluid discharge duct 45 extends from the control valve 40 to the oil sump 25.

Redundance elements

32, 33', 40, 41', and 32", 33", 40", 41" to increase the reliability of the system are connected in parallel to the

non-return valves

32, 33 and the associated control valves 40 and electro-magnet 41.

The control valve 40 is connected through a duct 42 and a distribution duct 43, on the one hand, through a duct 44 to a fluid duct 20 and, on the other hand, through a duct 51 to the duct 30 of the working cylinder 2. A non-return valve 50 is disposed in the duct 44 and a non-return valve 52 is disposed in the duct 51. These two

non-return valves

50, 52 have an oppositely oriented valve action. In normal operation of the plant, the non-return valve 52 remains closed by the pressure applied by a spring 52a therein and the fluid pressure in the

ducts

44 and 51 acting on the valve body 52b. The loading applied by the spring 50a on the valve body 50b of the non-return valve 50 is so selected that the control fluid can flow from the duct 20 without ob struction into the duct 44. The two

non-return valves

50, 52 represent a so-called selector circuit for the control valve 40, that is, the control valve 40 obtains a control fluid either from the pressure fluid duct 20 through the non-return valve 50 or from the duct 30 through the non-return valve 52, depending on the pressure prevailing in the pressure fluid duct 20.

The safety circuit operates as follows:

In normal operation of the system, the servomotor l is controlled by the control valve 13. The

non-return valves

32 and 33 are closed, the non-return valve 32 due to the action of the spring 32b acting on the valve body 32a and the non-return valve 33 due to the pressure of the control fluid which biases the right-hand side (as shown) of the piston 34. Since the valve 52 is closed, the control valve 40 is fed from the fluid duct 20 via the non-return valve 50, the connecting duct 44, the distribution duct 43 and the connecting duct 42. if a safety signal reaches the electro-magnet 41 from a suitable source, the plunger armature 41a will be attacted against the force exerted by the spring 41b. The control piston 40a of the control valve 40 thus moves to the right as viewed to connect the duct 42 to the non-return valve 33 so that the side 34a of the piston 34 is biased by pressure fluid and the side 34b is relieved of hydraulic fluid. Accordingly, the non-return valve 33 will open. It is thus possible for pressure fluid to be transferred from the duct 30 through the nonreturn valve 32 into the duct 31 and from there into the cylinder chamber 2b of the servomotor 1. Since the

ducts

30, 31 and the

non-return valves

32, 33 which connect these ducts, have a large cross-section, the effect of any possible after-feed through the control valve 13 is over-ridden so that the oil pressure on the piston side 3a diminishes rapidly and the piston 3 of the servomotor 1 moves rapidly upwards into the safety position due to the action exerted by the spring 10. The servomotor 1 will thus open the valve 6 and will have fulfilled its safety function.

If the supply of pressure fluid to the duct 20 should fail for some reason at the moment at which a safety signal appears at the electro-magnet 41 or if the oil pressure drops below a defined value, and in the event of the servomotor l failing to traverse under the effect of the spring 10 into the desired safety position, for example, due to ajammed control valve 13, because the oil pressure will then remain effective on top 30 of the piston 3, the non-return valve 52 will come into action. The valve body 52a of the non-return valve 52 will be relieved of the pressure fluid which normally is supplied from the fluid duct 20 through the non-return valve 44 to the duct 51, so that the non-return valve 52 is able to open. The control valve 40 will then be supplied with the pressure fluid disposed in the cylinder chamber 2a through the non-return valve 52 and the

ducts

51, 43 and 42. The control valve 40 will open the non-return valve 33 as described above so that fluid from the duct 30 will once again pass through the nonreturn valve 33 and through the non-return valve 32 into the duct 31 in order to reach the cylinder chamber 2b of the servomotor l. The piston 4 of the servomotor 1 will, thus, once again traverse into the safety position due to the action exerted by the spring 10. When the non-return valve 52 is opened, the non-return valve 50 is automatically closed by the fluid pressure prevailing in the duct 44 and thus prevents the control fluid from being lost through the fluid duct 20. The piston 34 is so dimensioned that the non-return valve 33 is reliably opened by a control fluid pressure which is obtained due to the action of the spring 10 immediately before the piston 3 is disposed in the cylinder chamber 2a.

Referring to FIG. 2, wherein like reference characters indicate like parts as above, the safety circuit can alternatively include two

non-return valves

60, 61 which are serially disposed between the

ducts

30, 31 connected to the cylinder chambers 2a, 2b, respectively, on both sides of the piston 3 of the servomotor I. One piston 62 of the non-return valve or check valve is connected to a valve body 64 which is biased to the left as viewed by a spring 63. The nonreturn valve 60 is controlled through a duct 70 from a hydraulic or pneumatic power amplifier in the form of a control valve 65 with a single-acting piston 68 or some other single-acting change-over element. The control valve 65 in turn is controlled by an electromagnet 66 in a balance circuit having a plunger armature 67 which is connected to the single-acting piston 68. The control valve 65 is connected through a duct 42' and the distribution duct 43 to the selector circuit, formed by the

non-return valve

50 and 52, and to the fluid duct 20.

In normal operation, when the non-return valve 60 is closed, the non-return valve 6H will prevent the nonreturn valve 60 from being opened when there is an adequate pressure difference between the cylinder chambers 2b, 2a imposed against the relatively slight thrust exerted by the spring 63, thus preventing pressure medium being transferred from the cylinder chamber 2b into the cylinder chamber 20.

Redundance elements

60', 65, or 60", 65", provided to improve the reliability of the system, are connected in parallel to the nonreturn valve 60 and the associated control valve 65. 14

The non-return valve 6k prevents pressure medium from 'being transferred into the duct section between the two non-return valves 61, 66 in normal operation when the non-return valve 60 is closed so that no leakage losses in the valve 60 can be transferred through its low pressure ducts. Since the power amplifier 65 has only one single-acting piston 68, pressure medium can leak only through this single-acting piston 68 to the low'pressure side of the system so that the leakage losses remain very small.

If a safety signal reaches the electro-magnet 66 to deactivate the electro-magnet 66, the piston 68 of the power amplifier 65 will release the connection through the duct 71) between the duct 42 and the non-return valve 60 so that the side 62a of the piston 62 is biased with pressure fluid. Accordingly, the non-return valve 60 will open. Pressure fluid may then flow from the cylinder chamber 2a of the servomotor ll connected to the duct 30 via the non-return valve 66, through its discharge duct 71l and through the non-return valve 61 into the duct 31 and from there may reach the cylinder chamber 2b of the servomotor 1 connected to the duct 3Il. The pressure on the piston side 3a of the servomotor 1 therefore diminishes rapidly and, due to the action of the spring Ml, disposed in the servomotor l and acting on the piston 3, the piston 3 then moves rapidly upwardly and into the safety position. At the same time, the servomotor 1 will open the valve (not shown) connected to the piston rod 4 and will have fulfilled its safety function.

if the supply of pressure fluid to the duct should fail or if the fluid pressure should drop below a defined value for any reason at the moment at which the safety signal appears at the electro-magnet 66, and, if moreover, the piston 3 of the servomotor ll fails to traverse into the desired safety position under the effect of the spring 10, the non-return valve 52 of this circuit will also come into action by opening. The power amplifier 65 will then be supplied through the non-return valve 52 and the

ducts

51, 43 and 412' with the pressure fluid disposed in the cylinder chamber 2a of the servomotor 1. The power amplifier 65 then opens the non-return valve as described hereinabove so that once again control fluid passes from the duct 30 through the nonreturn valve 60 and through the non-return valve 61 into the duct 31 and from there into the servomotor l. The piston 3 of the servomotor 1 will then once again move into the safety position due to the action exerted by the spring 110.

What is claimed is: 1. In a safety system a working cylinder (2) having a double-acting piston (3) dividing said cylinder into a first (2a) and a second (2b) chamber on opposite sides thereof; first control valve means (113) for selectively supplying pressure medium from a source of pressure medium (21) to either side of said piston (3) for moving said piston (3) between a safety position on that side of said cylinder pertaining to said first chamber (2a) and an operative position on the opposite side of said cylinder; power means (10) disposed in said cylinder to bias said piston (3) toward said safety position; duct means connecting said first and second chambers; first valve means (33) in said duct means and including actuator means (34) communicating said chambers (20, 2b) with each other in response to a safety signal; conduit means connecting said source of pressure medium and said first valve means; safety signal amplifying means (40) including a valve means and a signal responsive valve actuating means disposed in said conduit means to operate said actuator means to actuate said first valve means (33); passage means connecting said first chamber to said safety signal amplifying means; and automatic selecting means comprising a first nonreturn valve (50) in said conduit means and a second non-return valve (52) in said passage means selectively connecting said safety signal amplifying means (40) with said source of pressure medium (21) and with said first chamber (20) respectively. 2. The system as set forth in claim 1 wheren said first (50) and second (52) non-return valves (50, 52) are connected back-to-back with respect to each other.

3. The system as set forth in claim 1 wherein said power means is a spring mounted in said cylinder.

O UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,7516% Deted Sepnmber H 1913 -Inventor(s) RUDOLF R. ROHNER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, 'line 11, delete "14''.

I Signed and sealed this ll th day of May 197M.

(SEAL) Attest: v

EDWARD M .FLETCIERJR. C; MARSHALL DANN Attesting Officer Commissioner of Patents FORM PC4050 (IO-69) uscMM Dc 60316.:69 w u.s. GOVIVRNHENT PRINUNG orrlc: Ion o-au-su,

Claims

1. In a safety system a working cylinder (2) having a double-acting piston (3) dividing said cylinder into a first (2a) and a second (2b) chamber on opposite sides thereof; first control valve means (13) for selectively supplying pressure medium from a source of pressure medium (21) to either side of said piston (3) for moving said piston (3) between a safety position on that side of said cylinder pertaining to said first chamber (2a) and an operative position on the opposite side of said cylinder; power means (10) disposed in said cylinder to bias said piston (3) toward said safety position; duct means connecting said first and second chambers; first valve means (33) in said duct means and including actuator means (34) communicating said chambers (2a, 2b) with each other in response to a safety signal; conduit means connecting said source of pressure medium and said first valve means; safety signal amplifying means (40) including a valve means and a signal responsive valve actuating means disposed in said conduit means to operate said actuator means to actuate said first valve means (33); passage means connecting said first chamber to said safety signal amplifying means; and automatic selecting means comprising a first non-return valve (50) in said conduit means and a second non-return valve (52) in said passage means selectively connecting said safety signal amplifying means (40) with said source of pressure medium (21) and with said first chamber (2a) respectively.

2. The system as set forth in claim 1 wheren said first (50) and second (52) non-return valves (50, 52) are connected back-to-back with respect to each other.