Accumulator Sizing Sad
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Posted by: adeel.khan ®

01/04/2006, 13:31:09

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I am trying to size an accumulator to be used in Emergency Operation and on that basis I will size the Auxiliary pump. The system is being designed for a Crane Winch. The only data I have is the System pressure of 210 bar. How can I proceed with the calculations for the accumulator charging times and capacity.







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Re: Accumulator Sizing
Re: Accumulator Sizing -- adeel.khan Post Reply Top of thread Forum
Posted by: Kelly_Bramble ® Administrator

01/04/2006, 15:11:47

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See the following webpage; /hydraulic/accumulator_equations.htm







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Re: Accumulator Sizing
Re: Accumulator Sizing -- adeel.khan Post Reply Top of thread Forum
Posted by: jvan ®

01/04/2006, 14:26:12

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Sir,
I am assuming that you want to power a hydraulic winch motor
To size an accumulator circuit you need a minimum of data;

1.)the system pressure, in your case 210 bar

2.)The minimum pressure to do the work, if you are lowering the winch and gravity is helping you, the minimum pressure is probably the pilot pressure required to open any load holding valves that are in the system, counterbalance valves or overcenter valves.

If you are raising the load, then the minimum pressure will be the load pressure, this would have to be calculated or determined by using pressure gauges on both sides of the motor to determine the load pressure (differential across the motor).

3.)You also need to determine the volumne required, this can be determined by number of revolutions on the winch motor to lower the load times the displacement of the motor.

With this information you can use any of the sizing programs available on the web to size the accumulator, one of the easiest to use is Inphorm on the Parker Corp. website.
Good Luck,
John







Modified by jvan at Wed, Jan 04, 2006, 14:29:11


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Re: Accumulator Sizing
Re: Re: Accumulator Sizing -- jvan Post Reply Top of thread Forum
Posted by: adeel.khan ®

01/05/2006, 06:45:12

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Thanks John. This was great help. I got the formula for designing an accumulator as Auxiliary Power Source from the Parker Website. For me the P2 = 3045.792 psi, P3 = 435.1132 psi and P1 = 391.6019 psi (90% of P3).

I don't have any idea for the charging/discharging times for selection of f & n. I assume since the system is for Emergency Load Release, the discharging times would be very less.

With some assumptions, I have managed to calculate V1 (Volume of fluid collected or discharged by accumulator) = 146. 457 cubic.inches. What does this indicate? How can I select an Auxiliary pump (serving as a piggy back for another pump) on that basis?

Are accumulators selected on basis of Gas Volume or the Liquid Volume inside them?

What does the nominal capacity indicate?








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Re: Accumulator Sizing
Re: Re: Accumulator Sizing -- adeel.khan Post Reply Top of thread Forum
Posted by: jvan ®

01/05/2006, 12:02:28

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Thanks John. This was great help. I got the formula for designing an accumulator as Auxiliary Power Source from the Parker Website. For me the P2 = 3045.792 PSI, P3 = 435.1132 PSI and P1 = 391.6019 PSI (90% of P3).

........This means that the minimum pressure required to do the work is 435 PSI.


I don't have any idea for the charging/discharging times for selection of f & n. I assume since the system is for Emergency Load Release, the discharging times would be very less.

.......An accumulator will discharge as fast as you allow it, it is a function of the plumbing size and the valving. It is , in fact, an "expanding gas bubble" that is expelling the fluid.

With some assumptions, I have managed to calculate V1 (Volume of fluid collected or discharged by accumulator) = 146. 457 cubic.inches. What does this indicate? How can I select an Auxiliary pump (serving as a piggy back for another pump) on that basis?

.......This is saying that you need a total of 146 in^3 to do the work, i.e. if you were powering a 1 1/8 bore cylinder (approx. 1 in^2 area) with a 10 in stroke, for a total of 10 in^3 volume, you could stroke it approx. 14 times with your 146 in^3 of accumulator discharge. Since an accumulator follows the gas laws P1*V1=P2*V2; the early strokes would be at 3000 PSI, and the pressure would decay with each stroke to the minimum pressure of 435 PSI.

Are accumulators selected on basis of Gas Volume or the Liquid Volume inside them?
........Accumulators are selected by the discharge fluid volume required between the high pressure and the allowable low pressure. This is very simplified but if I needed 5 net gallons to do my work, move a cylinder, turn a motor etc. and my minimum pressure required to do the work was 1500 PSI and my system pressure, or the high pressure to charge the accumulator was 3000 PSI, I would need a 10 gallon accumulator. P1*V1= P2*V2, 10 gallons of gas at 1500 PSI(the precharge pressure) if I pump oil into the accumulator to a pressure of 3000 PSI, the gas volume will reduce to 5 gallons at 3000 PSI and I have 5 gallons of oil pressurized in the accumulator ready to do work. Sizing the pump is a function of the cycle time, as a standby you probably have a fair amount of time to load the accumulator. If all we are putting into the accumulator is 146 in^3 or approximately 1/2 gallon of fluid, the a 1/2 GPM pump would charge it in one minute, if you had to charge it in 30 secs, you would use a 1 GPM pump.

What does the nominal capacity indicate?
.....The nominal size or volume of the housing or bottle of the accumulator. A ten gallon accumulator will hold 10 gallons of gas/oil

The capacity of the system is required to be sufficient for:

•Activating / reset for at least 3 times in quick succession
........This again is a function of the net volume in the bottle.

•Continuous activation duration at least 3 minutes. When the system is activated, the limit switch for the low hook shall be automatically overridden.
.....I'm sorry; I'm not sure what you mean here.

050b472e








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