“3” indicates the spring of valve. Typical pilot-operated check valve applications include: stopping a cylinder in place when the directional valve is centered, holding a clamp in position, or maintaining a tool position. The relief valve opens when the combined force created by the pilot pressure and the load-induced pressure A check valve is used to allow fluid to flow back through the counterbalance valve without restriction. Checks vs. Counterbalance Valves. Command Controls’ counterbalance valves are supplied with a built-in check valve for free reverse flow from port 2 to port 1. It is a little more sophisticated than a one way restricting check valve. Operation The RP08A allows flow from port 2 to port 1, while normally blocking flow from port 1 to port 2. Prevent a load from drifting caused by directional control valve spool leakage. Required fields are marked *. Here are some guidelines for when it is most appropriate to use a P.O. Counterbalance valve or pilot-operated (P.O.) “7”indicates the check valve which will permit the flow of fluid during lifting the load but will restrict the flow of fluid during lowering of load. Waukegan, IL 60085 port of the counterbalance valve. LunchBox Sessions is a new take on online industrial training, full of interactivity, used by individuals, schools, and companies around the world. A counterbalance valve is a modulating valve that can maintain … If pressure at the cap end, and thus the pilot line, drops below the set point, the counterbalance valve partly closes to slow the platen. I’m very happy I found Your website. port of the counterbalance valve. • It is preferable that the valve be mounted close to the If a load must be controlled while in motion, a counterbalance valve should be used. Other options include a sealed pilot piston for master/slave cylinder applications and a vented spring chamber to atmosphere (which makes port 2 insensitive to backpressure) for servovalve or regenerative circuits. For load-holding and motion control, a counterbalance valve is the answer and worth the extra cost. A screw-in cartridge, poppet type pilot operated check valve for use as a blocking or load holding device. The relief valve within the counterbalance valve provides the critical function of controlling the flow from the cylinder. A counterbalance valve can easily be described as a pilot operated relief valve with a free flow check. Ph: (847) 680-8400 This site uses Akismet to reduce spam. They are not capable of metering the oil flow through them. Prevent a load from drifting caused by directional control valve spool leakage. The counterbalance valve will hold a load in position until pressure or an external force is applied to move the load. Do not use these valves with closed-center directional control valves. The load will not “run away” due to the effects of external forces, such as gravity. Pilot-operated check valves provide a leak-free seal, but counterbalance valves provide smoother operation when controlling the downward movement of a load. Counterbalance valves with pilot assist are meant to control an overrunning load. And couple design advises for both Pilot Operated Check Valves and Counterbalances Valves: Great article ! Pilot-operated check valves, or pilot-to-open check valves, are non-modulating valves and in operation should be considered either fully open or fully closed. This causes the valve to snap closed. The motion controller just can't handle the POCV opening and closing during normal operation. Counterbalance valves are used in hydraulic systems working with overriding (running-away) or suspended load. http://www.comatrol.com/application-notes, http://www.sunhydraulics.com/sites/default/files/media_library/tech_resources/TT_US_Ctrbal_POCk.pdf, http://www.qualityhydraulics.com/blog/load-holding-po-checks-or-counterbalance-valves/, http://apps.boschrexroth.com/products/compact-hydraulics/pib-catalogs/pdf/counterbalance.pdf. 70LPM pilot check valve cost. Therefore, they consist of a valve housing, a control piston for unlocking, a valve seat, a ball and a closing spring. B - Pilot assisted counterbalance valves with separate check valve and separate pilot piston The traditional design, often with parts in aluminium body (steel versions available in many cases), high flow capacity and compact dimensions, available in different sizes. Single Pilot-to-Open Check Valves. They both do the same job – don’t they? 3.28). Learn how a counterbalance valve works! Pilot Operated check valves should only be used in load holding or position holding applications where they work very well because of their typically near-zero leakage. Hydraulically pilot-operated check valves can, open requirement, open via an additional control oil connection in shut-off direction. (For this reason, counterbalances are often referred to as “motion control valves”.). In this case, the min. First of all, Pilot Operated check valves are NOT a cheap solution of Counterbalance valves. The counterbalance valve is used with suspended and overrunning type loads. In this type of situation, a pilot-operated check valve is an especially poor choice as it would cause the load to ratchet down as cylinder pressure is repeatedly built and released at the pilot “opening” pressure. In the circuit, you will find a check valve for free fluid flow, a relief valve for reverse flow and a pilot piston to lower the relief settings. pilot pressure, required to open the relief valve is 333 psi, i.e: Leak-free load holding. There will be one small pilot piston which will be attached with the bottom of spool of valve. Pressure trapped between the directional control valve and the actuator can pilot the counterbalance valve open and result in undesired load motion: Your email address will not be published. blocking or load holding device for flow rates up to 20 gpm (80 l/min) and 6000 psi (420 bar). When the operator begins to lower the load, this stored energy gives the counterbalance valve the message that a heavy load is on the boom, and less pilot pressure is required to open the counterbalance valve. A counterbalance valve will only open enough to allow the load to move at the desired flow rate, thus preventing the load from over-speeding the pump. Optional manual and flush manual release. This relieves the thermal expansion of oil, allowing the counterbalance valve to continue holding the load in the same position. check valve – which is best? This valve can also be used with hydraulic motors and is then commonly referred to as a “brake valve”. Whenever uncontrolled movement can occur from an overrunning load, a counterbalance valve should be used. The dynamic performance of a balance valve is many times better than the dynamic performance of a pilot operated check valve. 3) Pilot check on an equal area actuator. Pilot assist at port 3 lowers the effective setting of the relief valve … Do not use pilot-operated check valves with closed-center, directional control valves. For these applications consider using a counterbalance valve with 10:1 pilot ratio. I don't think you will have any problems with the POCV as long as the pilot is connected to the supply pressure. For load-holding and motion control, a counterbalance valve is the answer and worth the extra cost. In short, in pilot-operated check valves, the pilot pressure and load pressure act against each other, while in pilot-assisted relief valves, they act in the same direction against the spring. A control valve with a free flow (motor) spool should be used on any circuit which includes a Pilot Operated Check. Pressure trapped between the directional control valve and the pilot-operated check valve can pilot the check valve open and result in undesired load motion. Counterbalance valves are hydraulic devices that function using this basic principle: fluid can freely flow through a check valve into the actuator, and reverse flow will be blocked using a relief valve until a pre-set pressure is reached that is set based on the system pressure and load capability. Same thing. Furthermore, HYDAC pilot-to-open check valves are spring-loaded poppet valves. Blogs JLG said to replace counterbalance valve, which I did. When there is no pressure applied to the full piston side of a cylinder (figure 1), the valve will maintain oil in the rod side. Sometimes referred to as a “poor man’s counterbalance valve”, the P.O. Typical applications include: stopping a cylinder in place when the directional valve is centered, holding a clamp in position, or maintaining a tool position: When trying to lower a load being acted on by gravity, the Pilot Operated check may cause severe “ratcheting” of the actuator and resultant shock in the hydraulic system. The term 'pilot pressure ratio' is used to describe the internal area ratio of the valve. Use your pilot operated check valve for now. ... Counterbalance Valve None Pilot-Operated Check Valve A counterbalance valve is a modulating valve that can maintain an actuator movement at a desired flow rate. 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