Hook up drawing control valve
Hook up drawing of control valve
adding an externally drained pilot-operated check valve between the counterbalance valve and the cylinder will hold it stationary. 2-way directional control valves a 2-way directional valve has two ports normally called inlet and outlet. these are two of the three actions a directional control valve can perform. the backpressure check valve in the pump line maintains a minimum pilot pressure while the pump unloads. for air valves, atmosphere is the tank, so exhaust piping is usually unimportant. to operate a double-acting cylinder with 3-way valves, use the hookup shown in figure 8-32. pilot operated directional valves commonly use a check valve in the tank or pump line to maintain at least 50-75 psi pilot pressure during pump unload. in the situation shown here, it is obvious the relief valve will open before reaching a pilot pressure high enough to open the pilot-operated check valve. figure 8-52 shows the normal hookup of a 5-way valve. some 3-way valves have a third position that blocks flow at all ports. fluid free flows in one direction, but has controlled flow in the opposite direction. another flow condition is the diverter valve shown in figure 8-10. the following will describe how pilot-operated check valves can cause problems in some applications. mufflers not only make the exhaust quieter, but throttle the exhaust, which in turn controls cylinder speed in a meter-out circuit. when the valve shifts, as seen in figure 8-60, down force is 720 lb and up force is 800 lb.”) the float center valve of figure 8-43 allows the actuator to float while blocking pump flow. as b&g svtp pumps literature, manuals, cad drawings, detail. 4-way directional control valves figures 8-11 to 8-15 show different configurations available in 4-way directional control valves. using directional controls in ways other than normal is a common practice. check valves as directional valves normally a check valve is not thought of as a directional control valve, but it does stop flow in one direction and allow flow in the opposite direction. since the example selector valve is solenoid pilot-operated, it is important to determine which port has the higher pressure. heat exchangers, filters, and low-pressure transfer pumps often need a low-pressure bypass or relief valve. a 3-position, 4-way valve is more common in hydraulic circuits. this piping arrangement comes in handy in hydraulic circuits, since most manufacturers do not offer a 2-way valve. a water faucet allows flow or stops flow by manual control. if the crossover condition is important to the circuit or machine function, show it on the schematic drawing. this valve has a third position but there is no operator for it.
Fisher Control Valve Handbook
when the valve shifts to retract the fully extended cylinder, there is another problem. many valves use the two exhaust ports for speed control mufflers. to avoid running the pump dry, its shutoff should have a limit switch indicating full open before the electrical control circuit will allow the pump to start. a 5-way valve performs the same function as a 4-way valve. if a void in the cap of the cylinder is no problem then an anti-cavitation check valve is unnecessary. if the valve is solenoid pilot-operated, the supply to the pilot valve usually comes from port #1. also, a lot of 2-way hydraulic valves only stop flow in one direction, so they are useless in a bi-directional flow line. in figure 8-80, a running away load had a drifting problem with only the counterbalance valve installed. four 2-way valves may seem to be a complex and expensive way to operate a cylinder. using 2-way valves figures 8-22, 8-23, and 8-24 show some uses for 2-way directional control valves. by itself, a 2-way valve cannot cycle even a single acting cylinder. the number of boxes tells how many positions the valve has. to make a high flow 2-way valve from a 4-way valve try the circuit shown in figure 8-34. when using an on-off type solenoid valve, a fast moving cylinder stops abruptly when the directional valve centers. most hydraulic valves are a metal-to-metal fit spool design, so do not depend on the cylinder setting dead still with a tandem center spool. the counterbalance valve keeps the cylinder from running away no matter the flow variations, while the pilot-operated check valve holds it stationary when stopped. deenergizing the solenoid or retracting, lets the valve shift to home position, and the cylinder retracts from outside forces. figure 8-62 shows the symbol for a plain check valve. the longer the valve-to-cylinder lines are, the greater the air waste. they range from the simple, two-position, single, direct solenoid, spring-return valve shown in figure 8-11, to the more complex three-position, double solenoid, pilot-operated, spring-centered, external-pilot supply, external drain valve shown in figure 8-15. energizing and holding a directional valve solenoid causes the cylinder to move. in some actuator applications it is important to know what the valve port flow conditions are as it shifts. this valve is the pilot operator for hydraulically centered directional valves or normally closed slip in cartridge valves. figure 8-26 shows a circuit that operates a single-acting cylinder with 2-way valves. to stop an air cylinder in mid-stroke, use the 3-position valve shown in figures 8-19 through 8-21. the 5-way valve is found most frequently in air circuits. as shown in figure 8-69, a blocked center valve can actually cause a cylinder to creep forward.
COIL HOOK_UP KITS Balancing Valve Hook-up Kits Control Valve
metal-to-metal fit spool valves will not hold a cylinder for any length of time. vertically mounted cylinders with down acting loads always creep when using a metal-to-metal fit spool valve. also check with the manufacturer if there is any doubt about the valve’s performance in an unusual application. valve center conditions perform different functions in relation to the actuator and pump. placing a flow control after the pilot-operated check valve causes backpressure against its pilot piston and could keep it from opening at all. as b&g vtp pumps literature, manuals, cad drawings, detail. using 3-way valves in place of 2-way valves reduces inventory cost and saves time. with the flow control after the pilot-operated check valve, use one with an external drain. make sure the valve is capable of pressure in all ports before applying it to some of these circuits. this is the normal center condition for the solenoid valve on a solenoid pilot-operated, spring-centered directional valve. this valve shifts from an actuator moving flow path to center condition for certain special circuits. figure 8-49 shows an all ports blocked center condition, solenoid pilot-operated valve, as a simplified and complete symbol. the symbol in figure 8-68 shows a pilot-operated check valve with an external drain for the pilot piston. as pilot pressure builds to the 500 psi required, pressure against the poppet in the pilot-operated check valve increases at twice the rate. shifting the 2-way valve, or extending, sends fluid to the cylinder cap end and it extends. / m13 / m14 with v10i / v11i / v14i mass flow controllers. using a directional valve with blocked a and b ports in center condition, may keep the pilot-operated check valves open and allow cylinder creep. in either case it provides pilot pressure to shift the directional valves when a new cycle starts. if the cylinder extends with only one valve actuated, it would be slow and waste a lot of air. at about 150 psi the poppet in the pilot-operated check valve opens and allows oil from the cylinder rod end a free flow path to tank. a tandem center valve lets the pump unload while blocking the cylinder ports. energizing and holding a directional valve solenoid causes the cylinder to move. the pilot-operated check valve in the line to the cap end opens by pump flow like any check valve. lowering pressure at the rod end port is another way to save air with dual 3-way valves mounted directly to the cylinder port. an inline check valve stops any chance of reverse flow and is useful and/or necessary in many applications. to positively stop a cylinder, use a valve with the cylinder ports hooked to tank, and pilot-operated check valves in the cylinder line or lines. one (no) and one (nc) 2-way directional valve piped to the cap end cylinder port allows fluid to enter and exhaust from it.
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Control and Field Instrumentation Documentation
/ m13 / m14 with v10i / v11i / v14i mass flow controllers. even with some spool type counterbalance valves, the cylinder still drifts. figure 8-27 shows four 2-way valves piped to operate a double-acting cylinder. in normal condition, fluid in the control circuit exhausts through the exhaust port. using 5-way air valves the 5-way selector valve and shuttle valve in figure 8-50 works where a 3-way selector may not. 3-way directional control valves a 3-way valve has three working ports. the speed of exhausting air controls how fast the cylinder moves once it starts. this saves piping time and the cost of flow control valves. if the pilot-operated check valve poppet has load induced pressure holding it shut, plus reverse flow outlet port backpressure opposing the pilot piston, there is not enough pilot piston force to open the check poppet. a standard pilot-operated check valve circuit usually has minimum backpressure at the reverse flow outlet port. the anti-cavitation check valve has a very low-pressure spring, which requires 1-3 psi to open, so it allows tank oil to fill any vacuum void that might form. the following images show symbols of pilot-operated check valves that allow reverse flow. the decompression poppet releases trapped fluid in the piping between the pilot-operated check valve and the counterbalance valve allowing the main check poppet to open. most solenoid pilot-operated valves take air from the normal inlet port to operate the pilot section. the cylinder immediately runs away, pressure in cylinder cap port drops, the pilot-operated check valve closes fast and hard, and the cylinder stops abruptly. figure 8-2 shows a "normally open" (no) 2-way directional valve. here it is in the line feeding the directional valves, other times it is in the tank line. the complete symbol gives more information about the valve function and helps with troubleshooting and valve replacement. an all-ports open center condition directional valve unloads the pump and allows the actuator to float as shown in figure 8-38. as will be explained later, dual exhausts used for speed-control mufflers or as dual-pressure inlets make this configuration versatile. use this spring-centered, single solenoid valve in control circuits for special functions. some check valves have a removable threaded plug in them that may be drilled to allow controlled flow in the reverse direction. either valve moves the cylinder to its opposite position when activated. figures 8-5 through 8-10 show schematic symbols for 3-way directional control valves. a pair of 2-way valves at each cylinder port gives a power stroke in both directions. figure 8-51 shows a pair of 5-way valves piped to act like a three way light switch. a water faucet is a good example of a 2-way valve.
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figure 8-36 shows how to pressurize both ends of the cylinder when a 4-way valve centers. when solenoid b on the directional valve shifts, as seen in figure 8-72, the cylinder retracts. low backpressure from the check valve makes the cylinder creep forward at low power so the cylinder is in contact with a part before the next cycle starts. the all-ports-blocked center condition valve of figure 8-42 appears to block the cylinder ports. adding a flow control between the cylinder and pilot-operated check valve is one way to keep it from running away. except for bleeder type control circuits, a limit valve requires at least a 3-way function. both pauses that occur when extending and retracting are eliminated by using the dual-inlet feature of a 5-way valve. to unload the pump while blocking the cylinder from moving, use the valve shown in figure 8-46. this move eliminates the need for externally drained pilot-operated check valves. the extra hydraulic pressure pushes harder against the pilot-operated check valve poppet, making pilot pressure increase even more. when the pilot-operated check valve closes, pressure at the cap end cylinder port again builds to 150 psi, opening the check valve, and the process starts again. hsc-s literature, cad drawings, detail drawings,Installation manual, repair manual. this requires a high pilot pressure to open the pilot-operated check valve. to hold a cylinder stationary, it must have resilient continuous non-leaking seals, no plumbing leaks, and a non-leaking valve. even with some spool type counterbalance valves, the cylinder still drifts. the first four account for about 90% of all 3-position hydraulic valves in use. pump output is available for other valves and actuators with this center condition. shut-off valves are the only option for lines that flow out of the tank to a pump or other fluid using device. hi-l pump circuits, reverse free flow bypass for flow controls, sequence valves or counterbalance valves, and multi-pump isolation, to name a few. a check valve with a low-pressure spring, called an tank isolation check valve, on each return line allows free flow to tank, while blocking flow out of it. pilot-operated check valves figure 8-73 shows how using a pilot-operated check valve to keep a heavy platen from drifting can cause problems. a two position, single solenoid, spring return valve is sufficient for this operation. the center condition of a 3-position valve can unload a pump, open actuator ports to tank for free movement, block actuator ports to stop movement, give regeneration, or work in combinations of these functions. if the valve is solenoid pilot-operated, where does pilot supply come from? when the directional valve shifts, starting the cylinder forward, as shown in figure 8-74, pressure in the cap end cylinder port starts climbing to 150 psi. when solenoid a1 on the directional valve shifts, as seen in figure 8-71, the cylinder extends. when the tank is higher than the pump or directional valves, always install some means to block flow lines for maintenance.
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BOOK 2, CHAPTER 8: Directional Control Valves | Other
all return lines though, can have a check valve piped as shown in figure 8-65. the weight-to-cylinder force ratio and the rate of cylinder travel speed control the length of pause. a 2-way valve makes a blow-off device or runs a fluid motor in one direction.") all spool valves are five ported, but hydraulic valves have internally connected exhaust ports going to a common outlet. figure 8-54 shows a conventional 5-way valve hook up on a cylinder raising a 600-lb load. figures 8-41 to 8-46 show several commonly used 4-way hydraulic valve center conditions. pilot-operated check valves there are some circuits that need the positive shut off of a check valve but in which reverse flow is also necessary. deenergizing the solenoid, or retracting, lets the valve spring return to its normal condition causing the cylinder to retract. it is best to control the cylinder in this example with a counterbalance valve. it is best to control the cylinder shown here with a counterbalance valve. many of the circuits in this manual show standard check valves in use. a pilot-operated check valve with a decompression poppet would not help in this situation. adding an externally drained pilot-operated check valve between the counterbalance valve and the cylinder holds it stationary. on valves with other hardware added (here, pilot chokes and stroke limiters), it is better to show the complete symbol. the schematic drawing in figure 8-79 shows a cylinder with pilot-operated check valves at each port and meter out flow controls downstream of the reverse flow outlet port. control valves directional control valves perform only three functions: stop fluid flow allow fluid flow, and change direction of fluid flow. use a proportional valve with ramp timers to decelerate the actuator and eliminate shock damage. some 3-way valves select fluid flow paths as in figure 8-9. after shifting the valve, or extending, air flows from #1 port through #2 port to the cylinder cap end. a pilot-operated check valve with the decompression feature would not help in this circuit. with an external drain pilot-operated check valve, the pilot piston usually opens the check poppet to allow reverse flow. spool valves normally take pressure at any port without malfunction. shown are circuits that require a pilot-operated check valve to have external drain and/or decompression capabilities. a diverter valve sends fluid to either of two paths. connecting pressure oil to both cylinder ports and to each other regenerates it forward when the valve centers. in the past, to get this configuration, you only had to wire one solenoid of a double-solenoid, three-position valve. figure 8-3 shows a solenoid pilot operator using solenoid-controlled pressure from the inlet port to move the working directional spool.
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