Sequence valves block the oil to a secondary hydraulic circuit until pressure in the primary circuit reaches a preset level. The sequence valves have a built-in check system to allow the oil to flow back without external piping.Opening Pressure Check Valve (psi). I will fully guarantee these items. We have lots of hardware available - see my other auctions. Powered by SixBit's eCommerce Solution. This item is in the category "Business & Industrial\Hydraulics, Pneumatics, Pumps & Plumbing\Other Hydraulics & Pneumatics". The seller is "dockguys" and is located in this country: US. This item can be shipped worldwide.