After starting the pump, energize the directional valve and carefully raise the load a short distance. Excessive backpressure can damage a fast-turning hydraulic motor during an emergency stop situation. For example, counterbalance valves are used in some hydraulically operated forklifts. An open-center directional valve unloads the pump and keeps backpressure off the counterbalance valve outlet and pilot port. “Already today we have a very broad portfolio of solutions, which plays a vital role in combating climate change and air pollution. Both counterbalance valves and pilot-operated check valves can be used to lock fluid in a cylinder to prevent drifting. In addition, the pressure-actuated switch (9) will open the main motor run circuit should the pressure fall below a minimum value specified by the press manufacturer. Setting the counterbalance pressure approximately 25% higher than static pressure (1.25 × 566 = 707 psi) means that when pressure at the cylinder cap end rises to approximately 75 psi, the cylinder starts to stroke. If the upward acting force could be reduced or eliminated, the cylinder could do more useful work. 5-3: Internally/externally piloted counterbalance valveFigure 5-2 shows the symbol for an externally piloted counterbalance valve. Parker counterbalance valves are screw-in type cartridge valves that control the pressure at an actuator controlling its motion. Parker valves can be manual, motor actuated or solenoid air operated and electrically actuated, while mounting configurations can be sub-based, in-line or manifold. The 15,000-lb weight on the rod end increases the resulting downward force to 115,540 lb. The resultant downward force of 115,540 lb is an increase of 16% over the circuit with an internally piloted counterbalance valve. Any running-away or overrunning load needs some method to retard its movement. No matter how leak-free the counterbalance valve is, the internal bypass in the motor will let it slowly turn. Once pressure in the cap end cylinder line reaches 150 psi, the counterbalance opens and the cylinder extends. Internal pilot pressure opens the counterbalance valve enough for the cylinder to move. A counterbalance keeps an actuator from running away even with variable flow rates. Set the counterbalance approximately 100 to 150 psi higher than the load-induced pressure. The service requires full JavaScript support in order to view this website. They help manage pressure created by impacts and loads to help stabilize loads, avoid equipment damage and cope with hose failure and more. All rights reserved. Then continue turning the adjusting control in the same direction another to turn. May 29, 2018. Some designs take one eighth of the pilot pressure at the external pilot port as that set at the internal pilot port. The externally piloted system saves energy by eliminating all backpressure when performing work. A working counterbalance will hold the load suspended and gauge PG3 will show the load-induced pressure. Counterbalance valves can be used with paired cylinders: pilot pressure will open first the valve of the most heavily loaded cylinder; this will cause load transfer to the other cylinder and the related valve, still closed, will require less pilot pressure for opening. If the hydraulic motor tries to run away, say on a loaded winch, a brake valve holds against the load until the motors down port sees at least 113 psi. The counterbalance valve will hold a load in position until pressure or an external force is applied to move the load. Spool designs leak at a rate of 3 to 5 in.3/min, thus allowing actuator creep. www.hydraulicspneumatics.com is using a security service for protection against online attacks. Fig. This chatter usually applies to circuits with high load-induced pressure or when the counterbalance valve is mounted at a distance from the cylinder port. The cylinder would only extend when the counterbalance valve’s external pilot port sensed 1 psi at the cylinder cap end. 90° Fitting: connection point for the hydraulic hose. Optional manual and flush manual release. These are basically relief valves but used in a particular application to set up a back-pressure in a circuit. Figure 5-4 pictures a circuit with a running-away load. The difference between this circuit and a setup using a cross-port relief valve is that setting the brake valve at a pressure lower than system pressure does not affect normal actuator operation. When the cylinder begins to creep downward, increase the pressure until creeping stops. Fig. Uses include controlling over-running loads in cylinders and motors. Poppet designs leak at only 3 to 5 drops/min, minimizing cylinder creep. Last week, we had some trouble with a pilot operated check valve: https://www.youtube.com/watch?v=Frn3f1WZdLM. There is low oil level in the counterbalance system. Check for leaks on top of the counterbalance cylinder. Resetting the counterbalance valve keeps the cylinder from running away and reduces energy loss with a lighter load. Setting the flow control for maximum pump flow lets the cylinder run ahead when pump flow is low. Kim Fausing, President & CEO of Danfoss A/S, says, “Already today we have a very broad portfolio of solutions, which plays a vital role in combating climate change and air pollution. The following circuits show these characteristics and how to design around them. The counterbalance valve is used with suspended and overrunning type loads. Some manufacturers make counterbalance valves with internal and external pilots. © 2021 Endeavor Business Media, LLC. The end result is the same as the externally piloted valve of Figure 5-14. A brake valve appears virtually nonexistent as the motor runs under load. Now start lowering the counterbalance pressure setting slowly. Have you ever wondered... ...why Sun has four separate families of counterbalance valves? 1/4 and 3/8 NPTF Pneumatic Counterbalance Valves MODELS: 1/4 NPTF 3/8 NPTF No Manual Release B41C00 B61C00 Manual Release B41C0M B61C0M Flush Release B41CFM B61CFM Basic Operation: The counterbalance valve will hold a load in position until pressure or an external force is applied to move the load. Use an external braking system to hold any overrunning load driven by a hydraulic motor. Use an internally piloted counterbalance to hold a load back when the actuator does not need full power at the end of stroke. Externally piloting the counterbalance valve, Figure 5-14, requires about twice as much pressure to extend the cylinder. After the cylinder stops, pilot pressure builds again. The valve offers a resistance to the flow from the actuating cylinder when the fork is lowered. A vacuum void forms in the inlet side of the actuator that must be filled before applying force. This type of counterbalance valve retards flow continuously, so it resists flow even after work contact stops the actuator. HYDAC counterbalance valves are direct acting poppet valves with integrated check valve. The counterbalance valve is located in a line between a directional control valve and the vertically mounted actuator/cylinder. With the load suspended, deenergize the directional valve. When the cylinder contacts the work, all upward force is eliminated, minimizing energy loss. Turning the adjusting screw clockwise will increase the load carrying capacity of the valve. A counterbalance keeps an actuator from running away even with variable flow rates. The counterbalance valve working principle states that the fluid will be trapped inside the spool under pressure until the pilot pressure overcomes the pre-set value. Oil at high velocity leaves one end while the opposite side starves for fluid. 5-2: Externally piloted counterbalance valveFigure 5-1 shows the symbol for an internally piloted counterbalance valve. You will be redirected once the validation is complete. This orifice fix is difficult to get right and may cause other circuit problems.). They use the internal pilot to lower the load smoothly and the external pilot to drop all backpressure when performing work, thus avoiding loss of down force. (This is the same cylinder arrangement shown previously.) The counterbalance valve offsets the potential energy of the weight on the rod end of a cylinder. They help manage pressure created by impacts and loads to help stabilize loads, avoid equipment damage, and cope with hose failure and more. Advantages: Holding position, prevent runaway loads, pneumatic resistor. The cylinder holds in any position if the counterbalance valve is set correctly and does not leak. MODELS 1/2 NPFT 3/4 NPFT Approximately 7.5 tons of force from the rod end weight must be raised during every cycle but does not do any work as the cylinder extends. Learn how hydraulic counterbalance valves work. If flow to the cylinder cap end changes or even stops, cylinder speed responds accordingly. Some actuators with running-away (or overrunning) loads will let the load free fall when the directional valve that controls the actuator shifts to lower the load. 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