Accumulator volume problem 2

[ITBT]

I came across an accumulator volume problem that needs help.

I charged the an EPE AS55 accumulator from 0 to 4500 psi and turned off inlet valve. The pressure droped a little and stablized at 4000 psi. Then I opened outlet valve to collect water till pressure droped to 1600 psi.

In this case P1=1600 psi, P2=4500 psi, so accumulator precharge pressure P0=1300 psi. According to the chart, I expected the volume to be 24.5 litre, but only managed to get 17.5 litre.

Can anybody recomment on the shortage of volume. Thanks in advance.

 

[byrdj]

I could not find any "pressure/volume chart" for EPE As55 accumulator. I did find the EPE site that gave a few specs (

http://www.epeitaliana.it/standard.html).

The AS55 is a bladder type with a bladder volume of 50 liters. If the 50 liter gas bladder was pre charged to 1300 psig, then the fluid fluid side filled to 4000 psig, then the (PV)0=(PV)2 would be come 1300X50=4000XV2, therefore V2=16.3 liters. The fluid was drain to a pressure of 1600 psig, then the (PV)0=(PV)1 would be 1300X50=1600XV1, therefore V1=40.6. This gives a gas volume change of 24.3, which agrees with your chart.

If the bladder has a leak, and the precharge had reduce to 950 psig, then V2=11.9 and V1=29.7 and the volume change would be 17.8, which is near what you got.

I'm not that familar with bladder type, but another problem I've encounter with piston type has been fluid leaking into the gas volume and reducing it. In your case if 13.5 liters of fluid hasa leaked and reduced the initial gas volume to 36.5 liters.

Again not familar with bladder, but looking at EPE drawing, it looks like the bladder could be easily damaged if the fluid side pressure goes bellow precharge and the bladder extrudes around its stop.

in review, I would review EPE instructions to ensure not to damage bladder, then recheck the precharge. If it is 1300 psig, I would then try to invert and check for fluid on gas side.

 

[ITBT]

Thank you for your valuable comment. I checked precharge pressure once again and it was actually 1400 psi. Damage is not likely becourse there is a poppet valve to stop bladder from extruding.But how to check for fluid on gas side?

 

[byrdj]

When checking the precharge, is the fluid side open?

If you can invert the accumulator where the gas fill is down and then let some gas out would check for fluid in the gas side.

Again, I'm not that familar with bladder types and it has been many years since I work with the piston type, but I think some of the charteristics of a bladder is that they fail completely where as a piston can have the leakage problems. Also I though the operating range of the bladder is more limited. Like for a 4500 psig system the precharge is normally 80% (3600 psig)

You implied that EPE has a chart that states with a 1300 psig precharge, the operating pressure can be as high as 4500 psig. I can visulize a piston travelling with that range, but not sure what happens to the size of the bladder.

Is it possible that you have an AS35 with a 33.5 liter volume. With the pressures P0=1400,P1=1600, and P2=4000 and V0=33.5, the volume change would be 17.6 liters

 

[byrdj]

I found the following site that shows the error in my explannation and possibly in the epe chart.

http://www.fch.co.uk/products/acc_sizing_data.htm

the explanation with this chart is pretty good. this accumulator sizing chart assumes that the P and T will equalize from precharge to maximun pressure ( whick I also did) however this chart assumes the expansion from maximun to minumun will vary according to the properties of the gas (N2). My above calcs assume temp would equlize where this chart assumses a temp drop. using this chart, with a drop from 4500 to 1600 (p3/p2=2.8) and thier 54liter bladder, the discharge will be 17.2 liters.

Thus when you perform the discharge test, the accumulator temp may be dropping.

 

[ITBT]

Yes, it's ture. Thank you very much for your help.