Abstract: In the hydraulic system disclosed herein, a flow matching device is employed to implement a system in which filling, emptying and holding of a variable volume load, such as a hydraulic piston, may be accomplished at controlled flow rate by a hydraulic circuit including a flow matching control valve.

Abstract: A control valve includes a monolithic valve body incorporating dual digital valves and dual by-pass valves interconnected with each other by ducts within the valve body and providing for either controlled or uncontrolled actuation of a piston in either a forward or a reverse direction of movement.

Abstract: A servo valve comprising a source pressure valve whose inlet port receives a source pressure and whose outlet port communicates with the output of the servo valve, a pressure relief valve, which may operate independently from the source pressure valve, whose inlet port communicates with the outlet port of the source pressure valve and whose outlet port communicates with a pressure sink, for instance the atmosphere, and an electric circuit which controls both the source pressure valve and the pressure relief valve in such a manner that their actions are cooperative in a certain way. Since the source pressure valve and the pressure relief valves are not linked to each other by any mechanical means, the servo valve is very simple in its mechanical structure, fast in response, and does not require subtle mechanical adjustment.

Abstract: An actuator for controlling the pressure in an internal space defined by a spring-biased diaphragm and a housing by solenoid valve. The internal space is selectively communicated with a negative pressure port or an atmospheric pressure port through a first solenoid valve. The pressure in the internal space is determined by the ratio of a time period in which it is communicated with the negative pressure port to a time period in which it is communicated with the atmospheric pressure port, and the position of the diaphragm is determined accordingly. Another solenoid valve for releasing negative pressure is included for safety. To the housing fixed are a microcomputer for receiving status signals from a vehicle speed sensor, clutch ON/OFF sensor, brake ON/OFF sensor, etc. to generate a solenoid valve opening and closing signal, and a printed board incorporating an electrical driver adapted to energize the solenoid valve in response to said signal.

Abstract: The valve disclosed herein functions, in one sense, as a flow matching device and, in another sense, as a reciprocative check valve. By employing the valve, a hydraulic system may be implemented in which filling and emptying of a variable volume load, such as a hydraulic piston may be accomplished through a single check valve structure at controlled flow rates.

Abstract: In a pilot operated fluid supply valve the usual control pressure applied to the control surface of a main supply valve can be interrupted by a fluid switch and replaced with a pressure which closes the main supply valve. The fluid switch is responsive to the load pressure in the load port of the main valve. The fluid switch may include a rocker arm actuated by a diaphragm in fluid communication with the load port. In one system, main supply and waste diaphragm valves are controlled by a pilot valve and a pressure reversing valve, and the fluid switch is positioned between one of those valves and the main supply valve. In another system, the main valves are controlled by a dual output pilot valve.

Abstract: Supply and waste diaphragm valves communicate with each of two load ports 26, 28 and all valves are controlled by a pilot valve 78 and a pressure reversing valve 74. In one form, the pilot valve 356 has a rocker arm valve member 366. The pilot valve 78 applies high or low fluid pressure to control chambers 48, 64 and the control faces of two main diaphragms 40, 46, and it applies the same pressure to a diaphragm 90 which actuates the reversing valve 74. The pressure reversing valve 74 applies a reverse pressure to the control chambers 56, 62 and the control faces of the other two main diaphragms 42, 44. The pressure reversing valve 74 is a pressure actuated, supply and waste type valve in which the pressure applied by the pilot valve actuates a pressure driven element. The pressure driven element may be a diaphragm 90 or bellows 100. A higher control pressure is obtained with a ram nozzle 66 directed into the supply fluid at a point of maximum flow velocity.

Abstract: A four-way control valve comprises two side by side chambers 130, 132. Each chamber has high and low pressure inlet ports 151, 156, 157, 159 and an outlet port 162, 164. The high and low inlet ports of each chamber are alternately closed by respective flexible vanes 126, 128. The vanes extend through and pivot on walls 135, 137 of the chambers and the opposite ends of the vanes are joined by a linking bar 124. The linking bar is driven by a common actuator such as a solenoid 120. The pressures applied to the inlet ports of the chambers are inverted such that the pressures at the two outlet ports are opposite high and low pressures. The four-way valve may serve as a pilot valve 22 to actuate a higher flow capacity three or four-way diaphragm valve.

Abstract: A vacuum actuator having a vacuum chamber and an atmospheric chamber separated from each other by means of a diaphragm, and an actuator rod connected at its one end to the diaphragm and extending across the atmospheric chamber to the outside of the actuator so as to be connected to an object to be actuated. An annular solenoid coil is mounted on the upper surface of the upper wall of the case defining the vacuum chamber, in such a manner that the axis of the solenoid coil extends substantially at a right angle to the axis of the actuator rod. A plunger disposed in the annular solenoid coil is adapted to be moved in one and the other directions along the axis of the annular solenoid coil. The end of the plunger is adapted to be moved into and out of a valve case in which is defined a control pressure chamber.

Abstract: The servo-motor system is provided with an internal control line which communicates one control valve with a cylinder chamber which is connected to a control valve connected with an external control line. The internal control line permits the second valve to be actuated via the externally controlled control valve.

Abstract: An improvement in ball-type check valve arrangements including a valve body in which is formed a fluid passageway and a valve chamber communicating through a valve seat in the chamber, a ball in the chamber seated in the valve seat, and a reciprocal retaining member having a head engaging the ball in opposition to the valve seat and a stem extending from the head through the chamber wall opposite the valve seat, the ball and retaining member being reciprocably movable toward and away from the seat.

Abstract: This relates to a pneumatic feed system for moving a labeler head of a labeling apparatus for depositing labels in mold halves of a blow molding apparatus. The relatively heavy labeler head must be rapidly accelerated and then rapidly decelerated and at the same time moved sufficiently so as to provide for a large number of back and forth cycles per minute. There is provided in association with compressible shock absorbers a pneumatic system including a high pressure supply and a low pressure supply together with throttle valves such that the gas in the unpressurized end of the cylinder is rapidly compressed near the end of the stroke to function as a shock absorber and further, the cylinder is of a much larger diameter than that required for moving the labeler head so as to permit for the rapid acceleration as well as the rapid deceleration.

Abstract: A hydraulic control system comprising a hydraulic actuator having opposed openings adapted to alternately function as inlets and outlets for moving the element of the actuator in opposite directions and a variable displacement pump with loading sensing control for supplying fluid to said actuator. A pair of meter-in valves are provided to which the fluid from the pump is supplied and a pilot controller alternately supplies fluid at pilot pressure to a meter-in valve for controlling the displacement of movement of the meter-in valve and the direction and velocity of the actuator. Alternately pilot pressure from the pilot controller is applied simultaneously to both of the meter-in valves in conjunction with the venting of one of two load drop check valves to provide a regenerative mode.

Abstract: A pneumatic valve is disclosed, for controlling the position of a ram in a partly-extended condition. The valve has a combination of rubbing seals and diaphragms, for smooth operation and reliability. A spring-loaded plunger presses the diaphragm against the mouth of a port, to seal off the port. A piston with rubbing seals lifts the plunger from the diaphragm, to open the port. The piston seals rub against plastic, for freedom from water contamination problems, while the diaphragm provides the high integrity seal needed to control the ram position. A particular application of the valve is to the air control of dentist's chair, medical table or medical chair.

Abstract: The body of the braking valve includes a front chamber, an intermediate chamber and a rear chamber which surround a blocking component and a governing piston. The diameter of the bore, in which slides the governing piston at the rear of the chamber, is equal to the diameter of the line along which the truncated conical bearing surface of the blocking component comes into contact with a seat situated between the front and intermediate chambers. The pressure in the intermediate chamber is connected to an outlet of a distributor which has no effect on the balance position on the blocking component.

Abstract: A method of controlling a pneumatically operated servo-motor (1) having a linearly movable operating rod (6) is described in which the actual position of the operating rod is monitored continuously during each stroke, and when the rod reaches a position which lies a predetermined amount in front of a limit position reached during the preceding stroke the speed at which the operating rod travels towards the corresponding limit position of the current stroke is modified. In particular the method is used in a clutch actuating servo-motor to brake the speed of the operating rod at a position which corresponds to the initial contact between the clutch friction surfaces when the rod is moving to engage the clutch, so that the free travel of the clutch is taken up as quickly as possible, but the actual engagement is slowed in order to avoid undesirable jerkiness and wear.

Abstract: An improved control valve for double-acting piston and cylinder asemblies is disclosed in which pressure for actuating a regeneration valve to direct hydraulic fluid from the contracting side of the piston to the expanding side, is controlled by a cylindrical check valve apparatus (86-112) which surrounds the valve plunger and controls the pressure of fluid flowing from the contracting side to the reservoir.

Abstract: In a pulse modulated servosystem having solenoid activated on-off valves governing the amount of fluid in two variable volume chambers of a double-acting piston-cylinder unit any limitation of the accuracy due to inertia of the valves is eliminated by influencing both chambers in opposite directions.

Abstract: A closed center programmed valve system having a load sense fluid source for control of the raising and lowering of load means by a raise and a lower normally closed two stage valve assembly. Each of the second stages of the valve assemblies has a poppet with a parabolic contour which is dimensioned to provide substantially linear flow rate change for minimized shock when the respective valve is actuated to the valve closed state. The load sense for the load means is taken from the outlet of the raise second stage without the requirement of a separate actuated valve or land with a load sense signal being applied to the fluid source during the time the raise valve assembly is actuated to the valve open state.

Abstract: A closed center programmed valve system having a load sense fluid source for control of the raising and lowering of load means by a raise and a lower normally closed two stage valve assembly. Each of the second stages of the valve assemblies has a poppet with a parabolic control which is dimensioned to provide substantially linear flow rate change for minimized shock when the respective valve is actuated to the valve closed state. The load sense for the load means is taken from the outlet of the raise second stage without the requirement of a separate actuated valve or land with a load sense signal being applied to the fluid source during the time the raise valve assembly is actuated to the valve open state.

Abstract: A compressed-air operated dispenser for continuously dispensing a substance enclosed in a container, and in particular a viscous or paste-like substance, comprising an outlet passage extending from container to an outlet; a valve which normally closes the passage; a compressed-air operated piston arranged to exert pressure on a substance in the passage and to open the valve; and a trigger means for initiating the supply of compressed air for the purpose of operating said piston.In accordance with the invention there is provided a second valve arranged to move the piston to a starting position in which a pressure-actuating chamber is closed on one side of the piston with the exception of a passage through which compressed air can be forced into the chamber to cause the piston to move to a first terminal position. In this position the substance is subjected to pressure and the valve is opened and the piston ceases to act on the second valve.

Abstract: A hydraulic valve device for controlling a double action, piston-type servomotor adaptable for steering a self-propelled agricultural vehicle and including a pair of identical interconnected valve groups, with each group connected to an opposite side of the servomotor and further connected to a source of pressurized fluid and an exhaust outlet, whereby selective actuation of the hydraulic device creates a pressure difference in a servomotor forcing the piston to move in a predetermined direction.

Abstract: A high pressure hydraulic system, including a bidirectional fluid motor having two ports, a pair of normally closed, pilot operated poppet valves, each connected to an associated port, a fluid reservoir, a flow sensor having a flow path interconnecting each of the poppet valves and the reservoir and having an output for providing a signal representing the flow rate, along the flow path, a pair of metering valves each connected to the pilot of an associated poppet valve for controlling the flow of fluid through the associated poppet valve, control signal inputs for each of the metering valves, and flow rate signal inputs connected to the output of the flow sensor for each of the metering valves so that each poppet valve is ultimately controlled by both control signals and the flow rate through the flow sensor.

Abstract: A control circuit comprises pressurized fluid source (11), a two-position directional control valve (14) and an actuator (13), such as the pump of a hydrostatic transmission, connected to the fluid source and the control valve to be selectively actuated thereby.

Abstract: A relief valve assembly particularly in combination with yieldable pit posts is provided having an elongate housing, a first load chamber at one end of said housing, an inlet aperture into said housing, a non-return valve in said inlet aperture for admitting fluid non-returnably into said load chamber, a first valve seat in said housing communicating with said load chamber, a spring loaded relief valve movable lengthwise of the housing and normally engaging said seat to close the load chamber, a second valve seat in said housing spaced lengthwise from said first valve seat and relief valve and forming therebetween a balancing load chamber, a spring loaded pilot relief valve movable lengthwise of the housing and normally engaging said second seat to close the same, and a regulated orifice means in said relief valve connecting the first load chamber and the balancing load chamber whereby said balancing load chamber is normally pressurized to the pressure of the load chamber.

Abstract: Hydraulic control.The unit is characterized in that it is provided, between an inlet well and an outlet well for pressurized fluid, with an obturator urged in the closed position by a resilient member arranged to act against the pressurized fluid in the inlet well in a chamber communicating with a conduit issued from the outlet well and separated from a return conduit by a relief valve which is urged in the closed position by a spring and by the fluid pressure prevailing in the inlet well.Application to transfer-machines with one single hydraulic station.

Abstract: Method and device for braking the speed of movement of the piston of a plunger-cylinder device by choking the outlet of medium on the side of the piston approaching the end wall of the cylinder and by coupling the piston rod of the cylinder with the piston of a second plunger-cylinder device.

Abstract: A hydraulic system including a hydraulic motor having a port adapted to be connected to a reservoir and a hydraulic fluid pump. A normally closed check valve connects the port to the reservoir and includes two, hydraulically opposed, differential surfaces, one being smaller than the other and being disposed to be responsive to pressure at the port. Included is a normally closed, pilot-operated, first metering valve having an inlet and an outlet and a second metering valve also having an inlet and an outlet along with a shiftable metering element interposed therebetween. A spring biases the element towards a position minimizing flow between the inlet and the outlet and a pressure responsive surface is disposed on the element in bucking relation to the spring. The first valve inlet is connected to the second valve outlet and to a larger surface of the check valve and the port is connected to the second valve inlet as well as connected to direct pressure to the second valve pressure responsive surface.

Abstract: The closure and trip pilot valves of a circuit-breaker control unit are actuated by a hydraulic device controlled by a pressure drop which appears in control lines in response to the transient opening of a drain electrovalve within a control cubicle. Thus the pressure-drop hydraulic signal transmitted from a single central control cubicle for closing or tripping a circuit-breaker dispenses with the need for any electrical system and permits the control of a plurality of circuit-breakers or breaker modules solely by means of small-section lines providing hydraulic connections between the central control cubicle and each breaker control unit.

Abstract: A hydraulic control system comprising a hydraulic actuator having opposed openings adapted to alternately function as inlets and outlets for moving the element of the actuator in opposite directions and a variable displacement pump with loading sensing control for supplying fluid to said actuator. A meter-in valve is provided to which the fluid from the pump is supplied and a pilot controller alternately supplies fluid at pilot pressure to the meter-in valve for controlling the direction and displacement of movement of the meter-in valve and the direction and velocity of the actuator. A pair of lines extends from the meter-in valve to the respective openings of the actuator and a meter-out valve is associated with each line of the actuator for controlling the flow out of the actuator when that line to the actuator does not have pressure fluid from the pump applied thereto. Each meter-out valve is pilot operated by the pilot pressure from the controller.

Abstract: A valve controls fluid flow to a fluid jack by movement of a single valve spool to a first position. A check valve and bypass valve cooperate to pass fluid exhausted from the fluid jack to a tank bypassing the single valve spool. Movement of the bypass valve is controlled by developing a controlled pressure drop between the fluid in the fluid jack and the fluid between the check valve and the single valve spool in response to the valve spool being moved to a second position.

Abstract: A three-stage, four-section telescopic ram employing a plurality of internal fluid passages, with valving provided in certain of these passages, to produce a uniform overall extension speed when pressure fluid is supplied to the ram at a substantially constant rate.

Abstract: A control circuit for a hydraulic cylinder and shaft assembly to regulate movement of the shaft relative to one end of the cylinder. The circuit has a fluid pressure supply and associated reservoir and a metering valve with interconnected normally closed passage means connected at one end to the one cylinder end and at an opposite end to the reservoir. The fluid pressure supply, in a first condition, supplies fluid under pressure to the one cylinder end, and, in a second condition supplies piloting fluid under pressure for actuating the metering valve to regulate the fluid flow from the one cylinder end to the reservoir through the normally closed passage means.

Abstract: A compressed air engine having specially designed cylinder heads and piston configurations in order to reduce friction and maximize the application of air from a pressurized air source. The disclosure includes a lubrication system whereby the mechanical parts receive oil via a lubrication arrangement including a conveyor chain continually bathed in oil.

Abstract: A water cylinder compacting and squeezing apparatus has a control valve requiring a connection of only one tube to the water cylinder for driving and retracting the piston in the cylinder. A water cylinder is mounted to a frame having a removable container and a compacting or squeezing portion connected to a piston rod so that the water cylinder can be connected to the household water supply for squeezing or compacting foods or other materials. A water flow control system includes a first valve for turning on the flow of water which is directed into the water cylinder for driving a piston. A second valve allows the water to flow to the drain and create a suction to draw the water from the cylinder to return the piston. Once the piston is returned, the first valve shuts off the flow of water.

Abstract: A load check and bypass valve includes a check valve providing fluid flow from an inlet-outlet port to a motor port while blocking reverse flow therethrough and a bypass valve resiliently biased to a closed position for blocking fluid flow through a bypass connecting the motor port with the inlet-outlet port. The bypass valve has an opened position permitting fluid flow therethrough and is movable to its opened position by a selectively controllable actuating device. A first force exerting device is provided for exerting a force on the bypass valve urging it towards its opened position and is connected to the motor port by a first passage. A second force exerting device is provided for exerting a force on the bypass valve urging it towards its closed position and is connected to the motor port through a second passage. A check valve is disposed in the second passage providing fluid flow therethrough from the motor port to the second force exerting device while blocking reverse fluid flow therethrough.

Abstract: An expanding chamber hydraulic motor venting through a working member reduces the motor/stroke-limiting venting valve assembly to three simple components: a cup-shaped cylinder, an annular gasket at the open end of the cylinder, and undersize piston sufficiently loose in the cylinder to provide free-flow of hydraulic fluid therebetween but protruding through the gasket in a sealing fit; in operation, fluid pressure introduced by conventional means between the piston and cylinder can force the piston to extend from the cylinder only within a maximum stroke length limited by an annular groove around the piston which when it reaches the gasket vents the pressure past the gasket.

Abstract: A dual valve assembly having a charge and relief valve, comprising a unitary valve structure including a thick central body section and, extending therefrom, a pair of elongated hollow cylindrical valve members. A valve core is threaded into the bore of each valve member and a conventional valve cap is screwed onto the free end of one member, which end is adapted to be connected to an air source. A spring-biased plunger-cap or assembly is threaded onto the free end of the other valve member, the plunger being operable to engage the pin of the valve core at that end so as selectively to relieve the pressure. A passageway in the central section communicates with both of the bores and by a hose connection, with a pneumatic device whose operation is to be controlled.

Abstract: A valve system for controlling the direction of flow of pressurized fluid. The valve system includes a valve housing, with an inlet port for receiving pressurized fluid therein, a first cylinder port and a second cylinder port. The housing is further constructed with first and second exhaust ports. Passageways connect the inlet port to the first cylinder port and to the second cylinder port. Passageways also extend from the first cylinder port to the first exhaust port and from the second cylinder port to the second exhaust port. A pair of pistons and corresponding poppet valves are slidable within the housing to control flow of fluid through the passageways. In one embodiment, the pistons and poppet valves are moved by communicating fluid pressure from the inlet port either above or below the pistons. In an alternative embodiment, the pistons and popper valves are mechanically actuated.

Abstract: Control for a swing mechanism having linear actuators such as hydraulic cylinders connected to the swing mechanism in a manner whereby the actuators work in unison with each other over a portion of the swing of the swing mechanism and in opposition to each other over another portion of the swing when imparting arcuate motion to the swing mechanism with the linear motion of the actuators. The control includes a pressure reducing-metering valve and a metering valve in each of two sets of lines which supply and return pressurized fluid to the actuators. The respective valves limit the pressure of fluid to one actuator while requiring a predetermined minimum actuation pressure to provide a more constant speed and torque characteristic for the swing mechanism.

Abstract: A cable is connected between the dump body of a dump truck and the movable control member of an hydraulic valve to automatically shift the valve from its "raise" position to its "neutral" position when the dump body approaches its uppermost raised position. There is means to prevent inadvertent transmission of forces from the cable to the movable control member to thereby prevent accidental lowering of the dump body due to an inadvertent pull on the cable.

Abstract: An injection-molding machine has a drive ram with a pressurizable chamber that can be connected either to the high-pressure side or the low-pressure side of a source of fluid under pressure. A control system operating this machine has a pressure-reducing valve with an inlet port connected to the high-pressure side of the source, an outlet port connected through a cut-off valve and a throttle to the chamber of the ram, and a pilot port pressurizable to control the pressure at this outlet port. A pressure-relief valve has an inlet port connected to the pressurizable ram chamber, an outlet port connected to the low-pressure side of the pressure source, and a pilot port pressurizable to control the pressure differential across this pressure-relief valve.

Abstract: Backhoe swing apparatus including a backhoe swing bracket for supporting a backhoe for side-to-side swinging movement. A pair of hydraulic actuators are connected with the swing bracket for actuating the swing bracket in opposite directions. The hydraulic actuators are of the piston and cylinder type, and are controlled by a hydraulic system including a pair of hydraulic lines for conducting hydraulic fluid to and from each of the hydraulic actuators. A normally open pressure reducing valve in one of the hydraulic lines is operable to control pressure to one of the actuators to actuate the swing bracket in one direction and to thereby limit the pressure of fluid flowing to the actuator. Simultaneously, flow from the other actuator through the other hydraulic line is controlled by a first normally closed metering valve, which opens a permit such flow only when a predetermined minimum pressure exists in the other hydraulic line.

Abstract: The invention is a control system for a hydraulic clamping device adapted to be connected to a source of pressurized hydraulic fluid and to a hydraulically operated clamp, which system comprises a path for supply of pressurized fluid to and from the clamp, a check valve in the said path, a hydraulically operated pilot piston movable between a non-actuating position and an actuating position in which it urges open the check valve, means to hold the pilot piston in the actuating position and thereby maintains the check valve open and a switching means for controlling the supply of pressurized fluid to and from the pilot piston, the switching means being capable of occupying a neutral position, a position in which pressurized fluid is supplied to the pilot piston to urge the pilot piston to the actuating position to open the check valve and a position in which pressurized fluid is supplied to the pilot piston to return the pilot piston to the non-actuating position and thereby permit the check valve to close.

Abstract: An engine, or prime mover, utilizing the various expansion properties of a gas or fluid, hereinafter termed the "working fluid", for converting the pressures associated with said expansion properties into useful work. The engine having a "piston" and "cylinder" arrangement, with suitable valves, camshafts, etc., whereby expansion of the working fluid moves the "piston" exhibiting kinetic energy in accordance with the magnitude of the kinetic effects on the piston.

Abstract: A hydraulic interlock arrangement for ensuring that an inlet valve is closed before a discharge valve is opened, and vice versa, each inlet or discharge valve having a hydraulic piston-cylinder unit for actuating the same, a hydraulic pilot valve for operating the piston-cylinder unit and a blocking member for preventing actuation of the pilot valve, the first blocking member being connected to the pressure chamber of the second piston-cylinder unit, and vice versa, so that when the pressure chamber in one piston-cylinder unit is under pressure, the pilot valve of the other piston-cylinder unit cannot be actuated.

Abstract: An overrunning load control for a hydraulic jack includes a pair of variable orifice means in series, with the degree of metering of one of such orifices being determined by fluid pressure in the end of the hydraulic jack resisting the load. The degree of metering of the other variable orifice may be selectively chosen, through actuation of a relatively low pressure hydraulic pilot system.

Abstract: A servo mechanism for a prime mover interconnected to a hydrostatic transmission includes a source of pressurized fluid, a fluid reservoir, an actuator having a piston operatively connected to the hydrostatic transmission and being provided with large and small hydraulic receiving areas which are exposed to first and second hydraulic chambers, respectively within the actuator housing, a first passage for connecting the pressurized fluid source to the second chamber, a second passage for connecting the pressurized fluid source to the first chamber, a third passage for connecting the first chamber to the reservoir, and a pair of spool valve means disposed, respectively, within the second and third passages and responsive to a signal indicative of the power required of the prime mover and an actual speed or feedback signal of the prime mover.

Abstract: Fluid control systems for controlling machine tool operations or other automated mechanical devices. An unlimited number of multiple function systems can be assembled from a basic simple function system employing two-way relay valves which, in their normally blocked state, have a "controlled leakage" venting feature effective to prevent any leakage to outlet and possible system malfunction. Fluid memory can also be built in the system. Simple relay valves, limit valves, pressure control relay valves, time delay relay valves and other variations in spool and slide form provide controlled leakage.

Abstract: In order to provide a multi-way directional fluid flow control valve arrangement which provides good control while being relatively cheap to manufacture, I use simple main valves all of which have parallel axes and all lie in a common plane, enabling me to form the main valves in a cheap manufacturing operation; the pilot valve however is more complex and has at least four connections, but because the pilot valve is smaller, this extra complexity does not make the whole valve arrangement more expensive.