AU644504B2 - Safety valve - Google Patents

Description

AUSTRALIA

I

Patents Act 1990 COMPLETE SPECIFICATION For a Standard Patent

ORIGINAL

TO BE COMPLETED BY APPLICANT Name of Applicant: PBS ENGINEERING PTY LTD Actual Invenitcr(s.) :PHTTITP WATTS BRISTOW-STAGG Address for Service: WRAY ASSOCIATES, Primary Industry House, Terrace, PerLh, Wes-tern Australia, 6000.

239 Adelaide Attorney code: WR Inventi(on Title: "Safety Valve" Details of' Associated Provisional Applications: Nos: PK4 062 The foll3.owing statement is a full description of this invention, including the best method of performing it known to me: -1I- -2- THTS INVENTTON relates to a safety valve which has particular utility as a velocity fuse :in hydraulic Tn hydrauliJc ci rcui ts vahich i nc. u d a single or double S acinxg hydrauo'.ic cylinder in which the piston or ram i~s under 1 nad for -tended pern ads such as in c r anres a er t)h mov-inIg equipment o r the like, it i s generally a safety reqiy i .r eyre nt lbai a vk-l oci ty fuse be seri-ally connected T) i. Le irc I) wihsplies hydraulic fluid to the 1 0 cyl li der n order lo Jock ihe positi on of the pi ston or ram e Icl at i Ve t o !:li cylindte.r in the event; of the acc'de-ntI'.

I oss of- hydrau iic plrEIsDure such'1 Ha mJ gh1)t ari se I f Ih hydra."I 1 ios-e or pipe Icp yn he hydraulic fluid wuis to -I It VariooDs types,, or vel-oecily fuses have been d3esigned for thi s application, He inost poipulazr Jucorporatng a poppet, valve which is disposed in line with th)1E- pa ssage of hyd r auili c flid to 1_he oylinder and In no-rma,,l operatinug conditions is Iased away f romf a sea il lowing the normal fre flow o hydraiul ic f1.u i. clhethrough. In the event of a sudden hack Flow of 1 ui d, as wouild arise following a burs4t p) i e inr !Lice hiY> c connec ted In line with a piston or .ra)II und()er a n ext e rn aIIy app] -i (ed l oad, th1e po~ppet valve W o i'1 move t~o engage the seal-, thereby closing the ?9 hbydiri ic ciJrcuit in res ponse to the back flow of hydraulic flTi -rom -1e cyidr concerned, and consequently lock he relative posit.ion of the piston or ram within the cylinder, preventing thie load from moving the piston or ram further.

One problem with. this type of velocity fuse is that once 'the back pressure applied by -the pistLon or ram -to the hydraulic fluid in th~e cylinder disappears, the poppet valve will, again be biased away from the seat enabling -the 3 free flow of fluid to the cylinder once more.

Although) such an arrangement has utility when the burst hose or pipe is repaired, without the need for resetting the fuse, there is a problem when, after the fuse operates and locks the piston or ram position, that the load may bounce causing the back pressure in the cylinder to disappear momentarily. With this momentary release of back pressure, the poppet. valve will open once more allowing free flow of hydraulic fluid. If the operation of the veloc:ity fuse was caused by a loss of hydraulic fluid the hydraulic hose or pipe supplying t-he cylinder in the first place, then cl earl y once the back pressure is restored, the poppet valve would be forced o close once more. As a consequence, th e p i on or ram supporting the load would be locked again and the cycle repeal: itself. Indeed, the bounrinc:g effect of the load can continue in perpetu.i ty imposing great strains on the structure supporting the load. This perpetual bouncing effect of the load would also be accompanied by a gradual loss of fluid from the cylinder each time that the poppet valve was closed causiring the load to gradually overcome the resistance of tthi is,;ton or ram.

It is an object of the present invention to provide a safety valve for hydraulic circuits which can operate as a velocity fuse to mt:itigate the problems associated with locking the piston or ram relative to the hydraulic cylinder in the event of failure of the hydraulic circuit and where the load applied to the piston or ram is prone to bouncing upon such locking.

In accordance with a first aspect of the present invention, there is provided a safety valve for a hydraulic circuit comprising:- 4 a sleeve having an axial passage; a cylindrical chamber disposed within said passage and of larger diameter than said passage to form an annular seat with said passage; poppet mans retainedly disposed within said cylindrical chamber to be biased away from said annular seat with normal free flow of hydraulic fluid in said hydraulic circuit and to be biased towards said seat in response to a prescri bed back flow of hydraulic fluid; and locking means to lock said poppet means in juxtaposition to sa:id seat so as to close sa id passage to the flow of hydraulic flui.d Lherethrough after the occurrence of said prescribed back flow.

Preferably, said annular seat has an inner bore of smaller diameter than said passage and said poppet means has a spigot facing said seat, whereby said passage is closed upon said spigot forcedly engaging sai. inner bore.

Preferably, said locking means is provided by said spigot being tapered onvergingly towards said seat and said inner bore being of complementary taper, so that upon forced engagement between said spigot and said inner bore, said spigot is locked in juxtaposition with said inner bore by virtue of the residual friction between the engaging surfaces of these components.

In accordance with a second aspect of the present invention, there is provided a poppet means for a safety valve as hereinbefore defined, comprising a spigot convergingly tapered towards the outer end thereof, said taper being complementary to the taper of the inner bore of the annular seat of said safety valve.

The invention will be better understood in the light of the following description of one specific embodiment I 5 thereof, the description being made with respect to the following drawings wherein:- Figure 1 is a schematic view of a single acting hydraulic circuit which includes the safety valve; FiJgure 2a is a sclematic diagram of one form of double acting hydraulic circuit showing the position of the safety valve therein; Figure 2b is a schematic diagram of another form of double acting hydraulic circuit showing the position 1C of the safety valve; Figure 3 is a side elevation of the safety valve; Figure 4 :is a sectional view of the valve taken along section A-A of figure 3; Figure 5 :is an end view of the poppet as seen from the spigot end; Figure 6 is a sectional view of the poppet taken along section B-B of figure As shown in the drawings, the safety valve 11 generally comprises a sleeve body 1. an adjustment nipple 2, poppet means in the form of a poppet 3, biasing means 7n the form of a spring 4, a lock nut 5, an ring 6 and a backup ring 7.

The sleeve body 1 has a central axial passage 8 extending therethrough which is internally threaded a portional distance therealong at either end. One end of the valve body la is intended for direct ;onnection to the active port of a hydraulic cylinder 13 as shown in figures 1 and 2 and the other end Ib of the sleeve body threadedly accommodates the adjustment nipple 2. Accordingly, the adjustment nipple 2 is externally threaded a portional distance along the barrel thereof and is of commensurate size to the end of the passage to enable it to be screwed into the end Ib of the sleeve body.

6 A cylindrical chamber 9 is disposed intermediate of the threaded portion ends la and lb of the sleeve body 1 and forms part of the passage 8. The chamber 9 is of a marginally larger diameter than the threaded portion of the passage at the end of la of the sleeve body and is of a marginally smaller diameter than the threaded portion of the passage at the other end lb of the body which receives the adjustment nipple 2. The chamber 9 is provided to accommodate the poppet 3 and spring 4 axially of the adj ustment nipple.

The adjustment n:ipple 2 comprises a hollow barrel 15 having an outer flanged end 1.7 and has a grooved portion 19 at the inner end. The nipple 2 defines a central bore 21 which extends therethrough so as to be concentric with the passage 8 when th1e n:ipple :is screwed into position as shown in figure 4 of the drawings. The outer end of the bore 21 isi jnternal ly threaded a porl:ional distance therealong to enable screwed attachment to the hydraulic pipe 23 shown in figures 1 and 2 of the drawings.

The grooved portion 19 of the nipple is provided with an outer circumferential groove 24 which accommodates the "O" ring 6 and backup ring 7 in the manner shown at figure 4 of the drawings. The outer diameter of the grooved portion 19 of the nipple 2 is marginally smaller than the diameter of the cylindrical chamber 9 to enable location of the grooved portion therein when the nipple is screwed into position as shown in figure 4. Accordingly, the ring 6 has an outer diameter marginally greater than the diameter of the cylindrical chamber 9 to allow sealing thereof.

The grooved portion 19 also defines a constriction 25 of the inner bore 21 so as to form an annular seat 32 on uaarria~ I -sar 7 which the poppet may sit in a manner to be described in more detail later.

The poppet 3 is more clearly shown in figures 5 and 6 and comprises a shank portion 27 and a spigot portion 29, The shank portion 27 is of conventional form and comprises three vanes 31 radially disposed at approximately 1200 to each other to enable the passage of hydraulic fluid therethrough. The spigot portion 29 has a cylindrical distal nd 33 which is tapered convergingly a slight amount towards its end so as to form part of a locking means.

The other part of the locking means is provided by the outer end of the constriction 25 which has a complementary lhaped and ~zzed taper to the spigot end 33 to enable the spigot end to sit on the annular seat 32 when the poppet is moved towards :it. The sp):ring 4 sits between the outer end of the annular seat 32 and the inner end of the shank portion 27 of the poppet, thereby biasing the poppet 3 away from seating engagement with the annular seat 32.

As shown in figure 4 of the drawings, the cylindrical chamber 9 defines an annular shoulder 35 at its junction with the threaded portion of the passage 8 at the end la of the sleeve body 1 to retain the poppet 3 within the chamber.

Now describing the operation of the safety valve, the safety valve 11 is connected to the active port of the cylinder 13 as shown in figures 1 and 2 of the drawings at its end la and to the hydraulic pipe 23 at its other end lb. The hydraulic pipe 23 is connected to the main hydraulic valve 37 which is operable to provide an in flow of hydraulic fluid under pressure into the cylinder 13, or to allow a back flow of pressure from the cylinder 13, or 8to stop flow between the cylinder and the valve. The cyllunder 13 includes a piston 39 which supports a load 41, whereby free fl ow of hydrauli JaFlu:i d t~o the cylinder Causes the piston to elevater thle load 41 in both the single acoting 9 arnd d3oobl acting hydraulic circuits shown in figures I and 2.

The adojustment providedl by the sett:inug of the adjustmen-tL (Ai, )1 .Ppl 2 axiall1T1y rlaieto the sleeve body 1. allows Lte ts h o Id flIow r atIe th1iatt I he poppet 3 oVercomes th e r es i s L a iice-f o the spri ng 4 to be varied. Under normal op o, at 11g (c 3-1(J. I-i on s the Iload 41. its lowv ;ed by a ml le e Tlk- e of rin, C- 1,1 mfe. al. lo X3 og (sl role hc< l ow 'k1.roig'~he !3-,afety valve 1 1 ;ida: valve- 37.

To ;bhe ovnI FHa niilure oc cut r iin h:lyru pie 23 whi ch L- os hydryaul J, flu 1iid f.rom the(- c-I rcu1i t ,illowiog the hack presureprdu)Ced by the load to cause a r L api d, flow of hydraul ic flunid through the safety valve 11, t~he poppet 3 overcomes the resistancin -f the spring 4 by tje aiction of this ra-pid fl ow to an extent that the tapered 210 cyl1,in1dri1c al. end of the Spigot 33 engages wi th the compl e-ment Iary tapered por tion, o:f the annular seat. 32 Tn normA' caises, the increase in ha-Lck flow of hydraulic fluid causles r ap:i d mnio vemeniit of thc. poppet 3 'towards the v alve seal:1 32 so tha It ihe s-;p ig ot i s rapidly forced into 29 ungagement wi t. the inner bore of the valve seat locking the spigot in juxtaposition with the valve seat by virtue of the residual fri;cti on between the engaging surfaces of 11he( s te c om po n ents Upon. engagement C)f the spigot 33 with the va~vcz seat 32r the passage 8 is closed preventing further passago of fluid along the passage 8 of the valve body 1. As a result of the residual. friction between the engaging surfaces of the tapered port ion s of th1ie spigot and inner -9bre thec poppet remains lo~cked into position, even if th back pressure applied to the valve :fr om t he cylinde~r i s re-moved (o-I)ue t.1 y, the p opp1)e t wi T.It o nlIy b e .r e &aPe d u1pon a ctual. -re Se tti. nu either. by the application o:[ hydraul~i c fI lid under a forward pressure from the side of tho hydraumlic circuit coninected to the other end lb of -the I1 ~e V body, o~r by p-ressin-g the poppet out of engagement withI t-he valve seeat: by mecb.ic~il. mear-ns after the hydraulic pressure ha-s b~een r eleased from fthe passage 8.

As c an b e seen the del eteri .fAs effect: of A bouncing load o'pon the safety valve- Iselimin-ate-d by the locking aatJi on o1 U( tepoppet;- and st-at; Tt sold I he appreci atpd Ihat the scope of tl)e Anven ti on i s (ot r'i; e L 1-,c 1- embodiment described herein 1 5 emnId ac c ord(;In)gIy o ihe(-r Iypes of l oak ing means for l ockinrg t he poppet anrd seat of tihe siafely valve, toge be r may be msed wi t hou t departL inrg from t be spiri t of the iriven ta on.

Claims (3)

1. 3. A safety valve as claimed in claim 2, wherein said locking means is provi ded by sa-id spigot being tapered conve -gingly towards said seat and said inner bore being of complementary taper, so that upon forced engagement between said spigot and said inner bore, said spigot is locked in juxtaposition with sai~d inner bore by virtue of the residijal friction between -the engaging surfaces ot these components.
2. 4. A safety valve substantially as herein described in the embodiment. A poppet means for a safety valve as claimed in any orne of cla-ims 1 to 4, comprising a spigot convergingly tapered tc)widds thIie outer end thereof sa:i d taper being complementary the taper of the inner bore of the annular seat of said safety valve.
3. 6. A poppet means suibs Lantially as herein described ia the Dated this TWENTY-FOURPTH d3ay of DECEMBER 1991. PBS FNGT.NEERTNG PTY LTD Applicar.t WRAY AkSSOCTATES, Perth, Western Australia, Patent- Attorney-s for the Applicant, M I I i A safety valve (11) for a hydraulic circuit which includes a piston (39) and cylinder (13) operatable under a load The safety valve (11) includes a sleeve having a chamber disposed therein forming an annular seat (32) on which a poppet may sit. The poppet is biased away from the seat (32) with normal freeflow of fluid in the hydraulic circuit and is biased towards the seat in response a prescribed backflow of the fluid. Locking means is provided by the complementary shape of the &nnular seat (32) and spigot end (33) of the poppet (3) so that the poppet may be frictionally locked in juxtaposition to the seat (32) so as to stop the backflow of hydraulic fluid therethrough after the occurrence of the prescribed backflow.