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As ball valves they have zero leakage in the closed state. The directional. As ball valves they have zero leakage in the closed state. The directional. This can include their flow rate and pressure range, as well as the switching. FeaturesThe porting block makes it viable to utilize or connect several hydraulic lines from one pump to many tools as well as the possibility of connecting a pressure. FeaturesSpring cap and mechanical detent cap are made from die-cast aluminum. Parallel. FeaturesSpring cap and mechanical detent cap are made from die-cast. FeaturesSpring cap and mechanical detent cap are made from die-cast. Manual directional control valve. Standard on the air-oil booster UPM. Open centre. CETOP 3 base. Max pressure 700 barApplication. The NRV valves. The units can work. Eaton DG valves. They are available in both 3 way and 4 way styles. All versions are available in 2 position spring. It is a series type, and is recommended for all general purpose applications except lifting heavy loads in a vertical position. It will operate a double acting cylinder or a bi- directional. The proportional valves modulate hydraulic or motion parameters depending on electronic reference. There is a choice of electric, manual or hydraulic operating methods. Multiple operation. The valve can. Refer to application notes for installation details. Handle rotated full counterclockwise,. A great variety of auxiliary valves exists, fact that allows. The VL is a manual control valve that is capable of processing single and double acting systems. The VR, on the other hand, is a regulating. Thank-you for your help. Prices are indicative only and may vary by country, with changes to the cost of raw materials and exchange rates. Please try again.Please try again.Please try again later.In order to navigate out of this carousel please use your heading shortcut key to navigate to the next or previous heading.https://www.braveheartsforstrongminds.org/userfiles/bosch-maxx-7-sensitive-manual-english.xml
Register a free business account Amazon calculates a product’s star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers, and factors that establish reviewer trustworthiness. A 2-way valve stops flow or allows flow. A water faucet is a good example of a 2-way valve. A water faucet allows flow or stops flow by manual control. This requires a 3-way valve. A 3-way valve allows fluid flow to an actuator in one position and exhausts the fluid from it in the other position. Some 3-way valves have a third position that blocks flow at all ports. A 4-way valve pressurizes and exhausts two ports interdependently. A 3-position, 4-way valve stops an actuator or allows it to float. The 4-way function is a common type of directional control valve for both air and hydraulic circuits. A 3-position, 4-way valve is more common in hydraulic circuits. A 5-way valve performs the same function as a 4-way valve. Because oil must return to tank, it is convenient to connect the dual tank ports to a single return port. For air valves, atmosphere is the tank, so exhaust piping is usually unimportant. Using two exhaust ports makes the valve smaller and less expensive. As will be explained later, dual exhausts used for speed-control mufflers or as dual-pressure inlets make this configuration versatile. Following are schematic symbols for commonly used directional control valves. The at-rest box or the normal condition is the one with the flow lines going to and from it. In Figure 8-1, the active box shows blocked ports, or a closed condition, while the upper box shows a flow path. When an operator shifts the valve, it is the same as sliding the upper box down to take the place of the lower box. In the shifted condition there is flow from inlet to outlet. Releasing the palm button in Figure 8-1 allows the valve spring to return to the normal stop flow condition.http://www.e-skala.pl/userfiles/bosch-maxx-7-sensitive-manual-english.xml
A 2-way valve makes a blow-off device or runs a fluid motor in one direction. By itself, a 2-way valve cannot cycle even a single acting cylinder. Figure 8-3 shows a solenoid pilot operator using solenoid-controlled pressure from the inlet port to move the working directional spool. Figure 8-4 shows a cam-operated valve. A moving machine member usually operates this type valve. These ports are: inlet, outlet, and exhaust (or tank ). A 3-way valve not only supplies fluid to an actuator, but allows fluid to return from it as well. Figures 8-5 through 8-10 show schematic symbols for 3-way directional control valves. Figure 8-6 depicts an all-ports-blocked, 3-way, 3-position valve. A valve of this type connected to a single-acting, weight- or spring-returned cylinder could extend, retract, or stop at any place in the stroke. Another flow condition is the diverter valve shown in Figure 8-10. A diverter valve sends fluid to either of two paths. 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. Lines to the boxes show flow to and from the valve, while lines with arrows in the boxes show direction of flow. The number of boxes tells how many positions the valve has. This valve has a third position but there is no operator for it. Use this spring-centered, single solenoid valve in control circuits for special functions. In the past, to get this configuration, you only had to wire one solenoid of a double-solenoid, three-position valve. Figure 8-13 shows another unusual 4-way configuration. This valve shifts from an actuator moving flow path to center condition for certain special circuits. Most spool-type air valves come in a 5-way configuration. Because air usually exhausts to atmosphere, the extra exhaust port is no problem.http://www.drupalitalia.org/node/76071
Many valves use the two exhaust ports for speed control mufflers. Mufflers not only make the exhaust quieter, but throttle the exhaust, which in turn controls cylinder speed in a meter-out circuit. Also use dual inlet piping to make an air cylinder operate quickly and smoothly. (See Figures 8-48 through 8-55.) Most air cylinders stroke from one extreme to the other. A two position, single solenoid, spring return valve is sufficient for this operation. About 90 of air circuits use this type of valve. To stop an air cylinder in mid-stroke, use the 3-position valve shown in Figures 8-19 through 8-21. When the cylinder moves slowly, a repeatable mid stroke position of plus or minus an inch might be possible. The problem is, if the load on the cylinder changes or there is any slight leak in the piping or seals, it will not hold position once it stops. One use is the blow-off function shown in Figure 8-22. A 2-way valve in Figure 8-23 operates a one-direction motor with an open exhaust in the motor housing.Figure 8-25 shows a weight-returned, single-acting cylinder powered by a 2-way in the at rest condition. At first sight it looks as if this circuit might work. Shifting the 2-way valve, or extending, sends fluid to the cylinder cap end and it extends. The problem comes when the 2-way returns to normal at the end of cycle. Instead of the cylinder retracting after the solenoid de-energizes, it stays in the extended position. The cylinder would only return if the valve, cylinder seals, or pipe connections leak. One (NO) and one (NC) 2-way directional valve piped to the cap end cylinder port allows fluid to enter and exhaust from it. Actuating both operators simultaneously extends the cylinder. According to valve size and inlet air flow, the cylinder might not extend if just energizing the (NC) valve. If the cylinder extends with only one valve actuated, it would be slow and waste a lot of air. Figure 8-27 shows four 2-way valves piped to operate a double-acting cylinder.https://www.acnovate.com/images/4-stroke-scooter-service-manual-pdf.pdf
A pair of 2-way valves at each cylinder port gives a power stroke in both directions. Energize and de-energize all four valves simultaneously to cycle the cylinder and keep from wasting fluid. However, in the past few years, poppet type slip-in cartridge valves have been operating large bore hydraulic cylinders this way. See chapter four on Cartridge Valves for the advantages of these valves in high flow circuits. Using 3-way valves Figure 8-28 shows a 3-way valve, used to select Pr. 1 or Pr. 2. Use a spool type directional control valve in this type of circuit. Spool valves normally take pressure at any port without malfunction. Poppet design valves normally take pressure at the inlet port only. Most solenoid pilot-operated valves take air from the normal inlet port to operate the pilot section. If both inlet pressures are too low to operate the valve, plumb an external pilot supply from the main air system. Use a spool type valve here also. Poppet valves usually only take pressure at one port. This particular example is (NC). Contact with a machine member opens it. Except for bleeder type control circuits, a limit valve requires at least a 3-way function. In normal condition, fluid in the control circuit exhausts through the exhaust port. Energizing the solenoid, or extending, allows flow to move to the cylinder port and it extends. Deenergizing the solenoid or retracting, lets the valve shift to home position, and the cylinder retracts from outside forces. With a 3-way directional valve at both ports, both extend and retract strokes of a double-acting cylinder have force. Piping between the valve and cylinder ports wastes air. Every time a cylinder cycles, the lines to both ports fill and exhaust. The longer the valve-to-cylinder lines are, the greater the air waste. Mounting air valves directly to the cylinder ports minimizes air waste. The higher cycle rate results in greater savings.
As discussed before, reducing air pressure at the cylinder uses less compressor horsepower. Usually, force required to return a cylinder is minimal, so lower pressure at the rod port saves energy. This saves piping time and the cost of flow control valves. It is possible to inch an air circuit if accuracy and repeatability are not important.Faster travel speeds give less control. To duplicate the 2-way function, block the exhaust port of the 3-way valve. Blocking the exhaust of a 3-way is usually not necessary for most 2-way applications. Using 3-way valves in place of 2-way valves reduces inventory cost and saves time. Using directional controls in ways other than normal is a common practice. Make sure the valve is capable of pressure in all ports before applying it to some of these circuits. If the valve is solenoid pilot-operated, where does pilot supply come from. Also check with the manufacturer if there is any doubt about the valve’s performance in an unusual application. Connect pump flow to the normal inlet port and its outlet port, then connect the other outlet port to the normal tank port and on to the system. In the at-rest condition there is no flow through the valve. A valve rated at 10 gpm is now good for 20 gpm with little or no increase in pressure drop. Make sure the valve is capable of backpressure at the tank port. Also, a lot of 2-way hydraulic valves only stop flow in one direction, so they are useless in a bi-directional flow line. Read Chapter 17 for a full explanation of this regeneration circuit. Figure 8-36 shows how to pressurize both ends of the cylinder when a 4-way valve centers. When a cylinder retracts to pick up another part, it often has to go too far to make sure it is behind the part. 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. A double-acting cylinder only needs one 4-way directional valve to extend and retract it.
The three sequences show a 4-way valve in action. Add flow controls or a counterbalance valve to complete the circuit when there is weight on the rod. Note the port hookup is A to cap and B to rod. Maintenance persons always know which manual override to push during trouble shooting or setup. Valve center conditions perform different functions in relation to the actuator and pump. This reduces heat build up and allows opposing forces to move the cylinder without building backpressure. 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. If there are outside forces on the cylinder, it will creep when the valve centers. If the cylinder needs to float while blocking pump flow, use the center condition shown in Figure 8-40. The first four account for about 90 of all 3-position hydraulic valves in use. The open center condition unloads the pump and allows the actuator to coast to a stop or float. In the crossover or transition condition it causes very little shock. Fixed volume pumps use this center condition. The all-ports-blocked center condition valve of Figure 8-42 appears to block the cylinder ports. In actual use, leakage oil across the spool lands pressurizes A and B ports, possibly causing a single rod cylinder to extend. This is not a good choice for stopping and holding a cylinder as the symbol seems to indicate. 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. (See the section on “Check Valves as Directional Valves.”) Pump output is available for other valves and actuators with this center condition. It also works well for pilot-operated check valve locking circuits or with counterbalance valves. This is the normal center condition for the solenoid valve on a solenoid pilot-operated, spring-centered directional valve.
A tandem center valve lets the pump unload while blocking the cylinder ports. The cylinder sits still unless there is an outside force trying to move it. Any metal-to-metal fit spool valve never fully blocks flow. With external forces working on the cylinder, it may slowly creep with the valve centered. This is another common center condition for fixed volume pumps. Connecting pressure oil to both cylinder ports and to each other regenerates it forward when the valve centers. This valve is the pilot operator for hydraulically centered directional valves or normally closed slip in cartridge valves. However, the metal-to-metal fit spool will not lock the cylinder when there are external forces. In some actuator applications it is important to know what the valve port flow conditions are as it shifts. As shown in these figures, dashed lined boxes show crossover condition. Normally discussions about crossover conditions cover “open” or “closed” types; in reality, the crossover condition may be a combination of these and may be different on either side of center. Open crossover stops shock while the spool shifts, while a closed crossover reduces actuator override travel. If the crossover condition is important to the circuit or machine function, show it on the schematic drawing. On most schematics, the simplified symbol is sufficient. The solenoid slash and energy triangle in the operator box show the valve has a solenoid operated valve piloting a pilot-operated valve. The boxes show the function of the main or working spool that controls the actuator. On valves with other hardware added (here, pilot chokes and stroke limiters), it is better to show the complete symbol. Both symbols in Figure 8-49 represent the same valve. The complete symbol gives more information about the valve function and helps with troubleshooting and valve replacement. Internal pilot supply (X) and external drain (Y).
The 5-way selector valve and shuttle valve in Figure 8-50 works where a 3-way selector may not. The 3-way selector does fine when going from low to high pressure, but if there is no air usage to allow expansion, it is almost impossible to go from high to low pressure. After the air exhausts to the lower pressure, PR.1, the shuttle shifts and low pressure holds in the system. Either valve moves the cylinder to its opposite position when activated. Normally, input air goes to the center port of the side with three ports.The exhaust ports often have speed control mufflers to reduce noise and control the amount of exhaust flow. Speed control mufflers give individual meter-out speed control in each direction of travel. Use a spool type valve for this hookup, since it takes pressure at any port without malfunction. Putting low pressure on the rod side of the cylinder uses less compressor air without affecting the operation. This air savings results in lower operating cost and leaves more air to run other actuators. Install flow controls in the lines to the cylinder ports for individual speed control. On the circuit in Figure 8-53 a pilot line from system pressure goes directly to the pilot valve. System pressure goes into the external pilot supply port and a plug shuts off the internal pilot port. Changing the pilot line in the field with assistance from the supplier’s catalog is quite easy. Figures 8-54 to 8-61 show another reason for using dual pressure inlets. They depict air cylinder movement with conventional hookup. The cylinder pauses before raising and drops rapidly when starting to retract. Figure 8-54 shows a conventional 5-way valve hook up on a cylinder raising a 600-lb load. This figure shows weight, cap and head end areas, and pressures at both cylinder ports. The weight-to-cylinder force ratio and the rate of cylinder travel speed control the length of pause. The heavier the weight and the slower the cylinder speed, the longer the pause.
The delay could be three to four seconds in extreme cases. At the moment the valve shifts to extend the cylinder, down forces are up to 1240-lb while up force is only 800 lb. As long as down forces exceed up force, the cylinder will not move. The slower the air exhausts, the longer it takes to get enough differential pressure across the cylinder piston to move it. The speed of exhausting air controls how fast the cylinder moves once it starts. It moves up smoothly and steadily as long as the load remains constant. Figure 8-57 shows the cylinder at rest at the top. Up force is 800 lb from air pressure on the cap end, and down force is 600 lb from the weight. Now the load drops rapidly until air pressure in the cap compresses to approximately 120 psi. It takes about 120 psi on the 10-in.2 area to slow the cylinder’s rapid retraction. This sets a pressure differential across the piston before the valve shifts. The cylinder starts to move almost immediately and continues moving smoothly to the end. With the head end regulator set at 15 psi, down force from air pressure and the load is almost offset by up force. The load lowers smoothly and safely without lunging or bouncing, as fast as cap end air exhausts. In figure 8-59 to 8-61, the cylinder strokes smoothly and quickly in both directions with dual-pressure valve. These are two of the three actions a directional control valve can perform. Figure 8-62 shows the symbol for a plain check valve. Heat exchangers, filters, and low-pressure transfer pumps often need a low-pressure bypass or relief valve. A check valve with a 25-125 psi spring makes an inexpensive, non-adjustable, flow path for excess fluid. It protects low-pressure devices in case of through flow blockage. 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. Some manufacturers make a check valve with an adjustable spring, for pressures up to 200 psi or more.
The symbol in Figure 8-64 shows how to represent this in a symbol. A common use for a drilled check valve is as a fixed, tamper proof, flow control valve. Fluid free flows in one direction, but has controlled flow in the opposite direction. The only way to change flow is to change the orifice size. This flow control valve is not pressure compensated. Hi-L pump circuits, reverse free flow bypass for flow controls, sequence valves or counterbalance valves, and multi-pump isolation, to name a few. Figure 8-65 shows some other applications for check valves. When the tank is higher than the pump or directional valves, always install some means to block flow lines for maintenance. If the valves are not blocked, the tank must be drained when changing a hydraulic component. Shut-off valves are the only option for lines that flow out of the tank to a pump or other fluid using device. 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. All return lines though, can have a check valve piped as shown in Figure 8-65. 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. A check valve in the tank lines makes shut off automatic and eliminates chances of blowing a filter or wrecking a valve at startup. The backpressure check valve in the pump line maintains a minimum pilot pressure while the pump unloads. Here it is in the line feeding the directional valves, other times it is in the tank line. In either case it provides pilot pressure to shift the directional valves when a new cycle starts. An external force can pull against the trapped oil in the cylinder and cause damage or failure without relief protection. When outside forces move the cylinder, fluid from the rod end goes to the cap end, but is not enough to fill it.
If a void in the cap of the cylinder is no problem then an anti-cavitation check valve is unnecessary. However, this void can cause erratic action when the cylinder cycles again, so install an anti-cavitation check valve. 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 anti-cavitation check valve has no effect during any other part of the cycle. The following images show symbols of pilot-operated check valves that allow reverse flow. Figure 8-66 shows the symbol for a standard pilot to open check valve. Figure 8-67 shows a pilot-operated check with a decompression feature. The symbol in Figure 8-68 shows a pilot-operated check valve with an external drain for the pilot piston. Each of these pilot-operated check valves allow reverse flow, but two of them have added features to overcome certain circuit conditions. Metal-to-metal fit spool valves will not hold a cylinder for any length of time. As shown in Figure 8-69, a blocked center valve can actually cause a cylinder to creep forward. Vertically mounted cylinders with down acting loads always creep when using a metal-to-metal fit spool valve. Hydraulic motors always have internal leakage so the circuits shown here will not hold them stationary. Figures 8-70, 8-71, and 8-72 show a typical pilot-operated check valve circuit that prevents cylinder creep. When using an on-off type solenoid valve, a fast moving cylinder stops abruptly when the directional valve centers. Use a proportional valve with ramp timers to decelerate the actuator and eliminate shock damage. This center condition allows pilot pressure to drop and the pilot-operated check valves to close. 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.
If it is only necessary to keep the cylinder from moving in one direction, one pilot-operated check valve will suffice. Pump flow to the cylinder cap end builds pressure in the pilot line to the rod end of the pilot-operated check valve, causing it to fully open. The pilot-operated check valve in the line to the cap end opens by pump flow like any check valve. Energizing and holding a directional valve solenoid causes the cylinder to move. Pilot operated check valves positively lock the cylinder but are invisible to the electric control circuit. Pump flow to the cylinder rod end builds pressure in the pilot line to the cap end of the pilot-operated check valve, causing it to fully open. The pilot-operated check valve in the line to the rod end opens by pump flow like any check valve. Energizing and holding a directional valve solenoid causes the cylinder to move. In the example cited, a 15,000-lb platen pulling against a 26.51 square inch rod end area gives a 566 psi load-induced pressure. This load-induced pressure holds against the poppet in the pilot-operated check valve, forcing it closed. The pilot piston must have sufficient pressure to open the poppet with 566 psi pushing against it. The pilot piston on most pilot-operated check valves has an area that is three to four times that of the poppet. This means it will take approximately 141-188 psi at the cap end cylinder port to open the poppet for reverse flow. 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. 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. 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.
A cylinder with these conditions falls and stops all the way to the work unless it meets enough resistance to keep it from running away. However, the restriction could cause fluid heating and slow cycling, and would need frequent adjustment to maintain optimum control. With the flow control after the pilot-operated check valve, use one with an external drain. When there is much backpressure on the outlet of a pilot-operated check valve, it is best to use one with an external drain. See chapter five for the different types of counterbalance circuits. Adding an externally drained pilot-operated check valve between the counterbalance valve and the cylinder holds it stationary. 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. The cylinder in this example has a heavy weight pulling against the rod side. A load induced pressure of 1508 psi plus 142 psi from pilot pressure acts against the poppet in the pilot-operated check valve. This requires a high pilot pressure to open the pilot-operated check valve. As pilot pressure builds to open the poppet, it also pushes against the full piston area of the cylinder. This cylinder has nearly twice the area on the cap side as the rod side, so every 100 psi on the cap side gives about 200 psi on the rod side. As pilot pressure builds to the 500 psi required, pressure against the poppet in the pilot-operated check valve increases at twice the rate. Figure 8-77 shows the start of this condition. The extra hydraulic pressure pushes harder against the pilot-operated check valve poppet, making pilot pressure increase even more. In Figure 8-78, rod end pressure is at 3565 psi because pilot pressure continues to climb. 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.
Even if pilot pressure could go high enough to open the pilot-operated check valve, the cylinder runs away and stops. Flow from the small decompression poppet is not enough to handle cylinder flow. The cylinder would extend with a decompression poppet, but at a very slow rate. See chapter five for the different types of counterbalance circuits. Adding an externally drained pilot-operated check valve between the counterbalance valve and the cylinder will hold it stationary. 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. If there is a restriction causing high backpressure in the reverse flow outlet port, a standard valve may not open when applying pilot pressure. The reason this might happen is the pilot piston sees backpressure from the reverse flow outlet port. 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. Pipe the external drain to a low or no pressure line going to tank. With an external drain pilot-operated check valve, the pilot piston usually opens the check poppet to allow reverse flow. If this circuit did not have externally drained pilot-operated check valves, the cylinder would operate in jerks or not at all when the directional valve shifts. Backpressure from the flow controls can push the pilot piston closed and stop the cylinder, then pressure would drop and it would start again. This oscillating movement would continue until the cylinder competes its stroke. With externally drained pilot-operated check valves, the cylinder is easy to control at any speed. This move eliminates the need for externally drained pilot-operated check valves. Adding a pilot-operated check valve in front of the counterbalance valve stopped cylinder drifting.