So often I come across the problem of rams that creep out and this can be due to a few reasons.
Using a control valve with a centre position of all ports blocked is the most common cause. With this valve the blanked P port is under pressure and some leakage will pass either side to A&B, this will extend by displacing the rod area.
Another cause can be temperature. When the ram is locked in position using PO check valves or ball valves any temperature rise in the oil will cause expansion. If the piston seal is not 100% leak free the ram will creep forward. Without piston leakage the pressure could rise to an alarming value and cause damage to the ram.
Any load on a ram will make it creep over time. All valves have metal to metal sealing and the oil is the source of lubrication and leakage. As the running parts wear the leakage will increase and the ram will creep even more.
Always best to design with leakage in mind.
Cheers
Bob
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