Parker’s vented to atmosphere load holding/counterbalance valves are a combination of a relief, sequence, and flow control valve that can handle pressures up to 350 bar (5000 psi) and flows up to 113 lpm (30 gpm). These robust valves allow the operator to maintain control of the load by preventing it from overrunning the pump while also protecting against thermal expansion. The wide selection of pilot ratios enables the valve to open at pressures much lower than the spring pressure setting, allowing consistent control of the load throughout its lowering cycle. Because these valves spring chamber are vented to atmosphere, the valve will not be affected by changes in return pressure. Parker’s vented load holding valves are ideal in closed center circuits where there is need to control pressure using an auxiliary relief valve.

Markets:
• Aerial
• Construction Equipment
• Material Handling Equipment
• Miscellaneous Industrial
• Miscellaneous Mobile

Features/Benefits:
• Vented to atmosphere, no additional drain line required
• Hardened, precision ground parts for durability
• Poppet style construction with minimal leakage
• Tamperproof versions available
• Single cartridge valve with integral reverse flow check valve
• Available pilot ratios from 8:1 to 3:1
• All external parts zinc plated

Applications:
• Load holding
• Position holding

Additional Technical Insight:
The load control valves are load assisted i.e the pilot pressure acts on the difference between the setting and the load at the pilot ratio.
The valve should always be set at a minimum of 30% higher than the maximum load induced pressure to ensure the valve closes correctly.
Sizing a counterbalance valve needs care in that the flow required is usually higher than system pump flow, as in the case with a cylinder application (retract flow could be twice the system flow) though oversizing the valve could cause instability.
Because of  dynamic load variations in many applications, it may be necessary to use a lower pilot ratio or fit an orifice in the pilot line in order to gain stability.