Fluid flow control device and control circuit

Abstract

A fluid flow control device such as a volume booster has an inlet, an outlet and an exhaust port all for an operating fluid. A pilot inlet receives a pilot pressure signal which operates a valve stem actuator via a piston. The valve stem is operable to open a supply valve between the inlet and outlet and, separately and independently, to open an exhaust valve disposed between the outlet and the exhaust. In a further position both the valves are closed. Movement of the stem in a reciprocal manner by the piston causes a respective annular shoulder to engage a respective valve and lift it off a valve seat against the force of a biasing spring. A first fluid leak path is provided between the valve stem and the supply valve for allowing fluid to leak through the supply valve chamber when the supply valve is open and a second fluid leak path is defined by the exhaust valve for allowing fluid to leak through the exhaust valve chamber. The leak paths provide for a force balancing arrangement that allows the valve stem to move easily. A quick exhaust feature allows exhaust flow through the device instead of using a separate component. A regulated flow is provided to the actuator. The size of the exhaust port may be modulated by pilot control pressure.

1 . A fluid flow control device comprising: a housing defining an inlet, an outlet and an exhaust port all for an operating fluid; a pilot inlet for receipt of a pilot signal; a supply path in said housing that extends between the inlet and outlet; an exhaust flow path in the housing that extends between the outlet and the exhaust port; a supply valve chamber interrupting the supply path, a supply valve supported in the supply valve chamber for movement between an open position in which it permits fluid to flow through the supply valve chamber from the inlet to the outlet and a closed position where it prevents significant fluid flow through the valve chamber to the outlet; an exhaust valve chamber in the exhaust path, an exhaust valve in the exhaust valve chamber for movement between an open position in which it permits fluid to flow through the exhaust valve chamber from the outlet to the exhaust port and a closed position where it prevents significant fluid flow through the valve chamber to the exhaust port; a reciprocal actuating member in the housing and engageable with the supply valve and the exhaust valve for moving the supply and exhaust valves between the open and closed positions, the actuating member being movable, in response to a difference between the forces on the piston applied by the pilot signal and the outlet fluid pressure, between a first position in which supply valve is closed and exhaust valve is closed, a second position in which the supply valve is open and the exhaust valve is closed, and a third position in which the exhaust valve is open and the supply valve is closed; wherein there is a first fluid leak path defined by the supply valve for allowing fluid to leak through the supply valve chamber, a second fluid leak path defined by exhaust valve for allowing fluid to leak through the exhaust valve chamber, the housing containing a fluid filter between the inlet and the outlet. 
   
   
       2 . A fluid flow control device according to  claim 1 , the housing further containing a drain to allow for drainage of water. 
   
   
       3 . A fluid flow control device according to  claim 1 , further comprising a first biasing member for biasing the supply valve to the closed position. 
   
   
       4 . A fluid flow control device according to  claim 1 , further comprising a second biasing member for biasing the exhaust valve to the closed position. 
   
   
       5 . A fluid flow control device according to  claim 1 , where the supply and exhaust valve chambers each define a respective valve seat, the respective supply and exhaust valves being clear of the respective valve seat in the open positions and sealed against the valve seat in the closed positions. 
   
   
       6 . A fluid flow control device according to  claim 1 , wherein the supply valve comprises a poppet having a bore in which part of the actuating member is received, the first leak path being defined by a clearance between a wall of the bore in the poppet and the actuating member. 
   
   
       7 . A fluid flow control device according to  claim 6 , wherein the supply valve poppet is received in a support member, a supply valve seal being received between the poppet and the support member. 
   
   
       8 . A fluid flow control device according to  claim 7 , wherein the support member is in the form of a sleeve. 
   
   
       9 . A fluid flow control device according to  claim 1 , wherein the exhaust valve comprises a poppet having a bore in which part of the actuating member is received, the second leak path being defined by a clearance between a wall of the bore in the poppet and the actuating member. 
   
   
       10 . A fluid flow control device according to  claim 9 , wherein the exhaust valve poppet is received in a support member, an exhaust valve seal being received between the poppet and the support member. 
   
   
       11 . A fluid flow control device according to  claim 10 , wherein the exhaust valve support member is in the form of a sleeve. 
   
   
       12 . A fluid flow control device according to  claim 11 , wherein the exhaust valve sleeve has an outer surface and a sleeve sealing member disposed between the outer surface and an internal wall of the housing. 
   
   
       13 . A fluid flow control device according to  claim 1 , wherein the actuating member is an elongate valve stem reciprocally disposed in the housing and selectively and independently engageable with the supply and exhaust valves. 
   
   
       14 . A fluid flow control device according to  claim 13  wherein the valve stem has a first shoulder for engaging the supply valve such that movement of the stem to the second position causes the first shoulder to engage the supply valve and move it to the open position. 
   
   
       15 . A fluid flow control device according to  claim 14 , wherein the valve stem has a second shoulder for engaging the exhaust valve such that movement of the stem to the third position causes the second shoulder to engage the exhaust valve and move it to the open position. 
   
   
       16 . A fluid flow control device according to  claim 1 , wherein the pilot inlet is configured to receive a pilot signal in the form of a fluid pressure signal. 
   
   
       17 . A fluid flow control device according to  claim 1 , wherein there is provided a piston member connected to the actuating member and disposed so as to define first and second variable volume chambers in the housing, the first variable volume chamber being in fluid communication with the pilot inlet and the second variable volume chamber being in fluid communication with the outlet such that a pressure differential between the fluid in the first and second variable volume chambers causes the piston to move and the actuating stem to move between said first, second or third positions. 
   
   
       18 . A fluid flow control device according to  claim 17 , wherein the exhaust port is defined in the housing between the inlet and the second variable volume chamber. 
   
   
       19 . A fluid flow control device according to  claim 1 , wherein the filter comprises a porous member disposed between the inlet and the supply valve. 
   
   
       20 . A fluid flow control device according to  claim 19 , wherein the filter is cup-shaped. 
   
   
       21 . A fluid flow control device according to  claim 1 , wherein the drain is provided at a location under the filter. 
   
   
       22 . A fluid control circuit for operation of an actuator comprising:
 a main fluid flow line for connection to a source of pressurised fluid and for delivering pressurised fluid to the actuator at a first volumetric flow rate;   a volume booster in the main flow line having an inlet connected to the main flow line, an outlet for fluid communication with the actuator, an exhaust port for selective fluid communication with the outlet, and a pilot signal port for receipt of fluid control signals, the volume booster having a supply valve between the inlet and the outlet and an exhaust valve between the outlet and the exhaust, the valves being operable in response to a pressure difference between the pilot signal port and the outlet between first position in which the supply valve is closed and exhaust valve is closed, a second position in which the supply valve is open and the exhaust valve is closed, and a third position in which the exhaust valve is open and the supply valve is closed, the booster being configured to regulate the flow of fluid in the main flow line to the actuator;   a control flow line upstream of the volume booster and connected to the main flow line, for delivering control fluid at a second volumetric flow rate which is lower than the first volumetric flow rate;   a positioner in the control flow line and in fluid communication with a pilot signal port of the volume booster, the positioner being configured to deliver fluid control signals to the pilot signal port; and   a fluid regulator in the control flow line upstream of the positioner.   
   
   
       23 . A fluid control circuit according to  claim 22 , wherein there is provided a filter in the control flow line. 
   
   
       24 . A fluid control circuit according to  claim 22 , wherein there is no regulator provided in the main flow line upstream of the volume booster and downstream of the source of pressurised air. 
   
   
       25 . A fluid control circuit according to  claim 22 , wherein the volume booster has an integral filter disposed between the inlet and the outlet. 
   
   
       26 . A fluid control circuit according to  claim 22 , wherein the volume booster has an integral drain for draining water therefrom. 
   
   
       27 . A fluid control circuit according to  claim 22 , wherein the fluid regulator is disposed upstream of the positioner. 
   
   
       28 . A fluid control circuit according to  claim 22 , wherein there is provided at least one directional control valve between the positioner and the volume booster. 
   
   
       29 . A fluid control circuit according to  claim 28 , wherein the at least one directional control valve is stacked with the volume booster. 
   
   
       30 . A fluid control circuit according to  claim 22 , wherein the outlet of the volume booster is in fluid communication with an actuator for a valve. 
   
   
       31 . A fluid control circuit according to  claim 22 , the volume booster further comprising: a housing defining the inlet, outlet, the exhaust and the pilot signal port; a supply path in said housing that extends between the inlet and outlet; an exhaust flow path in the housing that extends between the outlet and the exhaust port; a supply valve chamber interrupting the supply path, the supply valve being supported in the supply valve chamber for movement between an open position in which it permits fluid to flow through the supply valve chamber from the inlet to the outlet and a closed position where it prevents significant fluid flow through the valve chamber to the outlet; an exhaust valve chamber in the exhaust path, the exhaust valve being disposed in the exhaust valve chamber for movement between an open position in which it permits fluid to flow through the exhaust valve chamber from the outlet to the exhaust port and a closed position where it prevents significant fluid flow through the valve chamber to the exhaust port; a reciprocal actuating member in the housing and engageable with the supply valve and the exhaust valve for moving the supply and exhaust valves between the open and closed positions, the actuating member being movable in response to a difference between the pressure of fluid at the inlet and the pressure of the fluid control signal at the pilot signal inlet; a first leak path defined by the supply valve for allowing fluid to leak through the supply valve chamber; and a second fluid leak path defined by exhaust valve for allowing fluid to leak through the exhaust valve chamber. 
   
   
       32 . A fluid control circuit for operation of an actuator comprising:
 a main fluid flow line for connection to a source of pressurised fluid and for delivering pressurised fluid to the actuator at a first volumetric flow rate;   a volume booster in the main flow line having an inlet connected to the main flow line, an outlet for fluid communication with the actuator, an exhaust port for selective fluid communication with the outlet, and a pilot signal port for receipt of fluid control signals, the volume booster having a supply valve between the inlet and the outlet and an exhaust valve between the outlet and the exhaust, the valves being operable in response to a pressure difference between the pilot signal port and the outlet between first position in which the supply valve is closed and exhaust valve is closed, a second position in which the supply valve is open and the exhaust valve is closed, and a third position in which the exhaust valve is open and the supply valve is closed, the booster being configured to regulate the flow of fluid in the main flow line to the actuator;   a control flow line upstream of the volume booster and connected to the main flow line, for delivering control fluid at a second volumetric flow rate which is lower than the first volumetric flow rate;   a positioner in the control flow line and in fluid communication with a pilot signal port of the volume booster, the positioner being configured to deliver fluid control signals to the pilot signal port;   wherein in the third position the exhaust valve is configured such that when pressurised fluid in the outlet exceeds the pressure of the pressurised fluid at the pilot signal port, the excess pressure is relieved through the exhaust port.   
   
   
       33 . A pilot-operated quick exhaust valve for exhausting fluid from a fluid actuator and comprising:
 a housing;   the housing defining an inlet port for connection to an exhaust of the fluid actuator, a pilot control port for receipt of a pilot control signal and at least one exhaust port;   a valve assembly reciprocal within the housing and comprising a piston connected to a valve member;   the piston being disposed in the housing to define on a first side of the piston a variable volume pilot pressure chamber in fluid communication with the pilot port and, on a second side of the piston, a variable volume inlet pressure chamber in fluid communication with the inlet port, such that the piston is moveable in response to a pressure difference between the pilot port and the inlet port;   the valve member being moveable with the piston between a first position in which it blocks fluid communication between the at least one exhaust port and the inlet port and a second position in which it opens the at least one exhaust port to allow for a maximum flow from the inlet and out through the at least one exhaust port;   wherein the valve member is biased to the first position by a biasing member, and movement of the piston in a direction such that the pilot pressure chamber decreases in volume moves the valve member towards the second position against the biasing force applied by the biasing member.   
   
   
       34 . A pilot-operated quick exhaust valve according to  claim 33 , wherein the valve member is penetrated by at least one passage to allow fluid to flow from the inlet to the inlet pressure chamber so as to act on the first side of the piston. 
   
   
       35 . A pilot-operated quick exhaust valve according to  claim 34 , wherein the valve assembly further comprises an elongate valve stem on which the piston and valve member are supported. 
   
   
       36 . A pilot-operated quick exhaust valve according to  claim 35 , wherein the piston is fixed to the valve stem and the valve member is movable relative thereto in the direction of a longitudinal axis of the stem. 
   
   
       37 . A pilot-operated quick exhaust valve according to  claim 34 , further comprising an outlet port in the housing, the outlet port being connectable to a supply port of the fluid actuator, and a supply valve member on the valve stem, the supply valve member being disposed between the inlet and the outlet ports and movable between an open position in which fluid can flow from the inlet to the outlet to pressurise the actuator and a closed position in which such flow is prevented. 
   
   
       38 . A pilot-operated quick exhaust valve according to  claim 33 , wherein the housing defines an internal wall disposed such that the inlet pressure chamber is divided into first variable volume chamber defined between the valve member and the internal wall and a second variable volume chamber defined between the other between the internal wall and the piston. 
   
   
       39 . A pilot-operated quick exhaust valve according to  claim 38 , wherein the internal wall is penetrated by at least one leak passage to allow fluid to flow between the first and second variable volume chambers. 
   
   
       40 . A pilot-operated quick exhaust valve according to  claim 38 , further comprising a biasing member for biasing the valve member away from the internal wall. 
   
   
       41 . A pilot-operated quick exhaust valve according to  claim 40 , wherein the biasing member acts between the valve member and the internal wall. 
   
   
       42 . A pilot-operated quick exhaust valve according to  claim 41 , wherein the biasing member is compression spring. 
   
   
       43 . A pilot-operated volume booster for controlling the volumetric flow rate of pressurised fluid from a source to a fluid actuator, the volume booster having a quick exhaust valve according to  claim 33 . 
   
   
       44 . A fluid control system for a fluid actuator comprising: a pressurised fluid supply line; an exhaust path; a pilot fluid control line for delivering fluid control signals; at least one pilot-operated quick exhaust valve according to  claim 33 , the inlet of the, or each, pilot-operated quick exhaust valve being connectable to an exhaust outlet of the actuator and the, or each, pilot control port being connected to the pilot fluid control line, the at least one exhaust port being in fluid communication with the exhaust path; and a volume booster for regulating the volumetric flow rate of the fluid to the fluid actuator, the volume booster having an inlet to the supply line, an outlet connectable to a supply port of the fluid actuator, and a pilot inlet connected to the pilot fluid control line. 
   
   
       45 . A fluid control system according to  claim 44 , wherein the volume booster has an integral quick exhaust valve according to  claim 33 .