GB2181821A

GB2181821A - Air dump valves

Info

Publication number: GB2181821A
Application number: GB08624804A
Authority: GB
Inventors: Brian Morrison
Original assignee: BERNARD STRUTT AGENCIES Ltd
Current assignee: BERNARD STRUTT AGENCIES Ltd
Priority date: 1985-10-16
Filing date: 1986-10-16
Publication date: 1987-04-29
Also published as: GB8624804D0; GB8525513D0

Abstract

An electro-pneumatic dump valve comprises an aluminium main body 12 section 2 and an aluminium block 3, a solenoid operated pilot valve assembly 4 being mounted to the former. Outlet 8 supplies pneumatic power to a remote machine and communicates to a main valve cavity 10 in which a valve shuttle 11 comprising poppets 13, 14 and associated cruciform connecting rod 12 is disposed for reciprocatory displacement. Input of air with poppet 13 seated and solenoid 31 activated produces a pressure differential between cavities 18 and 10 which urges the poppet into secure sealing seating. A bleed stream of air passes from cavity 18 via orifice 17 and bleed conduit 20 to pressure cavity 19, the pressure in the latter rapidly reaching the point where its force on poppet 14 balances the downward force on poppet 13. The seal of poppet 13 is then broken by the maintained pressure differential between cavities 10 and 18 to connect the air supply via cavities 10 and 18 to outlet 8. Poppet 14 is in this condition seated to isolate outlet 8 from exhaust 22. De-energization of solenoid 31 allows pressure in cavity 19 to act through solenoid conduit 29 on sealing disc 39 of the solenoid to open the solenoid outlet orifice 40 to atmosphere. This exhaust air and allows unseating of poppet 14 (and thus seating of poppet 13) which has the dual effect of shutting off air supply to cavity 10 from inlet 42 and of allowing entry of machine air by reverse flow back into cavity 10 via outlet 8 and its exhaust through exhaust outlet 22. <IMAGE>

Description

SPECIFICATION Improvements in and relating to air dump valves The invention relates to air dump valves for quick release of compressed air powering pneumatic equipment.

Developing force by an air piston has one distinct advantage over many electro/mechanical systems in that restricted movement can be withstood without damage From a safety point-of-view, however, this can have a dangerous side-effect, since any movement restriction in the form of a jam-up on a machine leads to a situation where the air cylinder acts as an air spring and could, to an unsuspecting operator, be storing a lethal force.

Accidents arising from such occurrences have led to a requirement in safety legislation for a means of quickly dumping air entrained within a system. Where a piece of equipment and associated circuitry as basic (eg a simple press with a guard) this can easily be achieved by a direct-acting valve with a spring return to the operating condition. More often than not, however, systems are more complex and generally involve interfacing with electrical controls and this leads to certain problems.

Whilst there are hundreds of different valves available it is difficult to find a valve or system of valves that, when interfaced with an electric circuit, does not rely on a mechanical spring or external force for return to a safe condition. The spring, although very basic, is generally disfavoured by the factory inspectorate.

Air dumping can acceptably be achieved using conventional valves if dual circuitry is employed. However, it is not the best solution because, by its very nature, it assumes that both circuits are functioning correctly when, in fact, the system could be runnint on only one.

It is thus necessary under safety legislation for a maintenance fitter periodically to verify the circuits and this is obviously undesirable in so far as the cost of labour is involved.

According to the invention, a dump valve for incorporation in a pneumatic circuit supply ing pneumatic power to a machine comprises (i) a valve body defining part of the pneumatic circuit between an inlet and outlet orifice of the dump valve, (ii) means defining an exhaust outlet, (iii) a valve assembly comprising an inlet valve member and a cooperating seat therefor both disposed between the inlet and outlet orifices with the member arranged to isolate the inlet and outlet orifices one from the other its seated position and to be displaceable between its seated and unseated positions, an exhaust valve member connected to the inlet valve member and displaceable with the inlet valve member between a first position in which the exhaust valve member is seated to isolate the exhaust outlet from the circuit outlet orifice and the inlet valve member is unseated to communicate the inlet orifice with the outlet orifice and a second position in which the exhaust valve member is unseated, the exhaust outlet is thereby in communication with the circuit outlet orifice and the inlet valve member is preferably seated so that the inlet and outlet orifices are isolated from each other, (iv) a bleed orifice in the valve body and opening to a bleed conduit connecting the inlet orifice to a pressure cavity defined in the valve body and housing the exhaust valve member so that pneumatic pressure at the inlet orifice is communicated to the pressure cavity and applied to the exhaust valve member to provide a pneumatic force opposing that applied to the seated inlet valve member through the inlet orifice of the valve body whereby the differential pressure between the inlet and outlet orifices is able to break the seal between the inlet valve member and its seat thereby releasing pressure on the inlet valve member and enabling that on the exhaust valve member to displace the inlet valve member from it seat, and (v) pressurerelief valve means for opening said pressure cavity to atmosphere so as instanteously to release the pressure therein and so to unseat the exhaust valve member, exhaust the outlet orifice pressure and preferably seat the inlet valve member.

The exhaust outlet will preferably comprise a plurality (eg four or more) conduits or passageways said passageways conveniently extending radially from a central cavity connected to the valve outlet orifice.

The valve assembly will conveniently comprise an upper poppet, alower poppet and a connecting rod, the assembly operating in a cylinder connecting the valve outlet orifice to an opening valved by the upper poppet and an opening valved by the lower poppet, the cylinder having a cross-section only partially occupied by the connecting rod so as to facilitate air passage. The connecting rod may be of cylindrical form with a circular or rectangular cross-section but will preferably be of cruciform configuration.

The pressure cavity housing the exhaust valve member (ie the upper or lower poppet in the arrangement just described, usually the lower poppet) will generally be provided with air-impermeable diaphragm to ensure prevention of air pressure leakage and thus application of pressure (on the diaphragm, the latter being in contact with the exhaust valve member) on the exhaust valve member.

The pressure relief valve means will generally be a solenoid valve in which a valve member is maintained in sealing relationship with an exhaust orifice from the pressure cavity by magnetic flux. The valve member may be a diaphragm or sealing pad displaceable by an armature member driven by flux from the solenoid coil. Exhaust of air from the pressure relief exhaust orifice may pass from the orifice through a gap between the coil and the armature member (eg. between a cylindrical armature member operating in a cylinder defined by the coil). However, this results in a danger of the necessarily small gap being blocked by debris entrained in the air and is generally regarded as unacceptable in a safety valve by strict safety regulation enforcement agencies.

The exhaust air should thus be directed to atmosphere by an alternative route. A preferred solenoid valve comprises an annular coil, an exhaust passageway extending from the pressure-relief exhaust orifice from the pressure cavity through (eg. axially) the interior of the annulus to an atmosphere outlet orifice, a sealing member carried by an armature plate (or driven thereby) displaceable by flux into sealing engagement over the atmosphere outlet orifice and by pneumatic pressure at said orifice to open said orifice to atmosphere in the absence of flux and means for retaining the sealing member and armature plate adjacent the said orifice in the open condition of the solenoid valve.

The following is a specific description, by way of example only, of one embodiment of the invention, reference being made to the accompanying drawings, in which: Figure 1 is a side view of an electro-pneumatic dump valve according to the invention; Figure 2 is a partially disassembled vertical cross-sectional view of the dump valve shown in Fig. 1; Figure 3 is a cross-section taken along the line Ill-Ill of Fig. 2; Figure 4 is a cross-section taken along the line V-V of Fig. 2; and Figure 5 is a cross-section taken along the line V-V of Fig. 2; The dump valve shown in the drawings comprises a right circular cylindrical valve body 1 comprising an aluminium main body section 2 and an aluminium inlet block 3.

Block 3 is secured to section 2, and the two parts (Fig. 2) of the latter are secured together by four screws (Figs. 3 and 4) equispaced on a pitch circle and extending parallel to the valve axis. A solenoid valve 4 is mounted to the main body section 2, the steel- right circular cylindrical casing 5 of the solenoid valve 4 having a mounting flange 6 penetrated by a series of fixing bolts 7 (Fig. 2) engaged in the main body section 2 at spaced positions around a pitch circle.

Main body section 2 is formed with a pneumatic outlet 8 internally threaded to receive and engage a coupling of an outlet line 9 (Fig.

1) supplying a pneumatically powered machine (not shown). Outlet 8 communicates with main valve cavity 20 in which a valve shuttle 11 is disposed for axial reciprocatory displacement.

Valve shuttle 11 comprises a connecting rod 12 of cruciform configuration terminating in an inlet valve poppet 13 and an exhaust valve poppet 14. Internally of main body section 2 surfaces are provided to define inlet valve seat 15 and exhaust valve seat 16.

A pneumatic bleed orifice 17 opens into inlet cavity 18 and connects cavity 18 to void 19 by means of bleed conduit 20, the orifice 17 being of substantially narrower cross-section than that of the conduit 20. The two sections shown of the conduit 20 are drilled in the main body section 2, closure screw 21 being provided to seal the radial section of the conduit from atmosphere.

A plurality of radial exhaust outlets 22 connect main valve cavity 10 to atmosphere, depending on disposition of exhaust valve poppet 14. An annular gauze muffler 23 is located in grooves 25, 26 formed in circumferential recess 24 to dispense exhaust air issuing from outlets 22 in use of the dump valve.

A neoprene diaphragm 27 is provided in the main body section 2 to provide a pneumatic seal isolating the void 19 from main valve cavity 10. The diaphram is sandwiched between mating parts 2a and 2b of the main body section 2, the latter being secured together by six screws (not shown) spaced apart on a pitch circle and penetrating the 2a 2b interface. An opening in diaphragm 27 facilitates communication between void 19 and bleed conduit 20.

Inlet block 2 is formed with an inlet orifice 42 which, in the assembled dump valve, connects air supply to inlet cavity 18 of main body section 2 from a remote pneumatic source (not shown). Orifice 42 is internally threaded to receive and engage a coupling of an inlet line 43 (Fig. 1). As shown in Fig. 1, the lower flange 44 of a mounting bracket 45 is secured to the upper surface of valve inlet block 3. An auxiliary inlet 46 is provided offcentre through the top of the inlet block 3.

Outlet conduit 28 from main body section 2 communicates void 19 with central exhaust bore 29 formed in column 30 of solenoid valve 4. The latter houses annualarresin-encapsulated coil 31 energizable by power supplied from a remote source via power lead 32, pins 33, 34 and plug 35 (Fig. 1). Circular recess 36 houses a perforated cover plate 37 and an armature plate 38 interfacially secured to a neoprene sealing disc 39 for the outlet orifice 40 of central exhaust bore 29, the assembled components just referred to being retained in recess 36 by circlip 41.

In use, with the pneumatic power source and pneumatically powered machine shut down, the condition of the dump valve will be as shown in Fig. 2. In this condition, it will be seen tat inlet valve poppet 13 is seated on valve seat 15 so that inlet orifice 42 from the pneumatic power source is isolated from main valve cavity 10 and outlet 8, the latter being open to exhaust outlets 22 and orifice 40 being open to atmosphere. In order to bring the dump valve into operation, solenoid coil 31 is energized whereby flux from the coil draws armature plate 38 to it so that neoprene disc 39 seals outlet orifice 40 of bore 29. Pneumatic power is then supplied to the machine via the dump valve by activating the remote pneumatic power source. Air is thus supplied via line 43 and inlet orifice 42 to inlet cavity 18 of main body section 2.Seating of poppet 13 on seat 15 ensures air does not pass into main valve cavity 10 to the outlet 8. As pressure increases in cavity 18 poppet 13 is urged more securely onto its seat 15 by the pressure differential between cavity 18 and cavity 10 to improve the valve poppet seal and so to resist the greater pressure. Air is also passed via bleed orifice 17 and bleed conduit 20 to void 19 beneath diaphragm 27.

After a short time lag, airpressure in void 19 is sufficient that diaphragm 27 exerts a force on valve poppet 14 equal to that exerted in inlet cavity 18 on inlet valve poppet 13. This depletes the valve seating effects of the cavity 18-cavity 10 pressure differential just mentioned. At this point, the same pressure differential causes air to 'crack' the seating of inlet valve poppet 13, thus releasing pressure to main valve cavity 10 and outlet 8. The pressure release produces an instantaneous differential between the force on inlet valve poppet 13 and that exerted on exhaust valve poppet 14 by diaphragm 27 whereby shuttle 11 is immediately displaced upwardly until exhaust valve poppet 14 seats on lower valve seat 16.

In this condition of the dump valve, valve poppet 13 is, of course, wide open and air supply passes from inlet cavity 18 to main valve cavity 10 (whose cross-section is only partially filled by the cruciform configuration of the connecting rod 12) to supply outlet orifice 8 and thence, via line 9, to the machine. This represents the normal operating condition of the dump valve.

When an emergency machine shut-down is required, electrical power supply to solenoid valve coil 31 is cut off. In the resulting absence of flux, neoprene sealing disc 39 releases under gravity and air pressure from its sealing position over orifice 40 of bore 29 whereby pressure in void 19 is instantaneously released to atmosphere. The resulting removal of the force applied to exhaust poppet 14 causes the poppet to unseat under the force of air supply acting on the crown of poppet 13 in inlet cavity 18. Main valve cavity 10 is thus connected to exhaust orifices 22 through which pneumatic machine pressure is dumped, shutting down the machine. Poppet 13 seats and thus shuts off air supply to outlet orifice 8, line 9 and thus the machine. This condition of the dump valve is typically achieved after no more than 15-20 milliseconds after deactivation of the solenoid coil 31.

The invention as described earlier without reference to the drawings may include any one or more features of the invention as described with reference to the drawings.

Claims

1. A dump valve for incorporation in a pneumatic circuit supplying pneumatic power to a machine, the valve comprising (i) a valve body defining part of the pneumatic circuit between an inlet and outlet orifice of the dump valve, (ii) means defining an exhaust outlet, (iii) a valve assembly comprising an inlet valve member and a cooperative seat therefor both disposed between the inlet and outlet orifices with the member arranged to isolate the inlet and outlet orifices one from the other in its seated position and to be displaceable between its seated and an unseated position, an exhaust valve member displaceable with the inlet valve member between a first position in which the exhaust valve member is seated to isolate the exhaust outlet from the circuit outlet orifice and in which the inlet valve member is unseated to communicate the inlet orifice with the outlet orifice and a second positiin in which the exhaust valve member is unseated the exhaust outlet is thereby in communication with the circuit outlet orifice and the inlet valve member is seated so that the inlet and outlet orifices are isolated from each other, (iv) a bleed orifice opening to a bleed conduit for connecting the inlet orifice pressure to a pressure cavity defined in the valve body and so disposed in relation to the exhaust valve member that in use pneumatic pressure at the inlet orifice communicated to the pressure cavity applies a consequent force to the exhaust valve member in opposition to that applied to the seated inlet valve member through the inlet orifice of the valve body whereby differential pressure between the inlet and outlet orifices is able to break the seal between the inlet valve member and its seat thereby releasing pressure on the inlet valve member and enabling that on the exhaust valve member to displace the inlet valve member from its seat, and (v) pressure-relief valve means for opening said pressure cavity to atmosphere so as substantially instanteously to release the pressure therein and so to unseat the exhaust valve member, exhaust the outlet orifice pressure and cause seating of the inlet valve member.

2. A dump valve as claimed in Claim 1 wherein the exhaust outlet comprises a plurality of conduits or passageways, said passageways extending radially from a central cavity connected to the valve outlet orifice.

3. A dump valve as claimed in Claim 1 or Claim 2 wherein the valve assembly comprises an upper poppet, a lower poppet and a connecting rod, the assembly operating in a cylinder connecting the valve outlet orifice to an opening valved by the upper poppet and an opening valved by the lower poppet, the cylin der having a cross-section only partially occupied by the connecting rod so as to facilitate air passage.

4. A dump valve as claimed in Claim 3 wherein the connecting rod has cruciform cross-section.

5. A dump valve as claimed in any preceding claim wherein the exhaust valve member is provided with air-impermeable diaphram to ensure prevention of air pressure leakage and thus ensure application of force on the exhaust valve member.

6. A dump valve as claimed in any preceding claim wherein the pressure relief means is a solenoid valve in which a valve member is maintained in sealing relationship with an exhaust orifice from the pressure cavity by magnetic flux.

7. A dump valve as claimed in Claim 6 wherein the solenoid valvecomprises an annular coil, meansdefiningan exhaust passageway extending from the pressure-relief exhaust orifice from the pressure cavity through the interior of the annulus to an atmosphere outlet orifice, a sealing member driven by an armature plate and displaceable by flux into sealing engagement over the atmosphere outlet orifice and by pneumatic pressure at said orifice to open said orifice to atmosphere in the absence of flux, and means for retaining the sealing member and armature plate adjacent the said orifice in the open condition of the solenoid valve.

8. A dump valve for incorporation in a pneumatic circuit supplying pneumatic power to a machine, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.