By MHS Posted 11th April 2017
WELCOME TO OUR NEW FEATURE FROM OUR HEAD OF OPERATIONS AND HYDRAULICS GURU… WE BRING YOU NEIL’S KNOWLEDGE
Neil joined us at the end of 2016 coming from a long and successful career in marine hydraulics. As such we would like to share some of that experience and knowledge with our clients...
So Neil, what causes a creep in a double-acting cylinder?
'A creep in a double-acting cylinder is caused by a leaking piston seal. A popular misbelief about hydraulic cylinders is that if the piston seal is leaking, the cylinder can creep down. Right and Wrong. The fact is, if the piston seal is completely removed from a double-acting cylinder, the cylinder is completely filled with oil and the ports are plugged, the cylinder will hold its load indefinitely - unless the rod-seal leaks. What happens under these conditions? Due to the differences in volume either side of the piston, is fluid pressure equalizes and the cylinder becomes hydraulically locked. Once this occurs, the only way the cylinder can move is if fluid escapes from the cylinder via the rod seal or its ports. If you grasp the theory at work here, you'll probably realize there are a couple of exceptions. The first is a double-rod cylinder - where volume is equal on both sides of the piston. And the second is when a load is hanging on a double-acting cylinder. In this arrangement, the volume of pressurized fluid on the rod side can be accommodated on the piston side. In this case a vacuum will develop on the piston side and depending on the weight of the load, this may eventually result in equilibrium that arrests further creep.’
Neil Duffield, Marine Hydraulic Solutions