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  • hydraulic cylinder design - pressure

    Discussion in 'Calculations' started by tonycro, Sep 19, 2016.

    1. tonycro

      tonycro Well-Known Member

      Nov 2011
      Likes Received:

      Being moved out of my material comfort zone and into fluids after a job change; and in need of some basic advice.

      we have a pneumatic driven oil unit that can develop 700b and a flow rate of 5.3cc/stroke. The cylinder that is being supplies is a double acting design 2" bore and 1" rod dia, to open a 660lb vessel lid and the cylinder is rated to to 200b.

      In an effort to reduce the stroke time the supply pressure was allowed to run to maximum - even I know that pressure dies not give speed !

      But the question, if the pump is design to give an output of 700b - will the system see that pressure or will only see the the pressure generated by the resistance due to the load ?

      many thanks
    3. Nclopton

      Nclopton New Member

      Sep 2016
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      You are correct. The hydraulic system will see only the pressure required to move the load plus the pressure loss caused by the piping system itself. However, if the cylinder reaches its end of stroke, the hard stops on the cylinder will act like a stationary load and cause the hydraulic pump to apply its maximum pressure on the system in an attempt to move the cylinder. I recommend installing relief valves and safety valves to prevent the system from over pressurizing in the event you reach the end of stroke on the cylinder (or if you have a larger load than anticipated or a closed valve in the system). You might also be able to include an end of stroke sensor that shuts off the pump or diverts hydraulic fluid back to the reservoir (by means of an automated 3-way valve).
    4. Dana

      Dana Well-Known Member

      Sep 2010
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      Did you mean 700 and 200 psi? If the cylinder is rated 200psi and the pump can produce 700, bad things will happen unless either have a relief valve or you reduce the pneumatic supply pressure to keep the hydraulic pressure within the cylinder's rated limit.

      Regardless, the actual pressure depends on what the limiting factor is. The pressure could go over the actual load due to inertial effects if the fluid is supplied fast enough.

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