Hello everyone,,

Please need help How to charge accumulator that is empty? For gas turbine frame 6.

If we have:
1. charging & gauging assembly.
2. Nitrogen bottle 20 bar of pressure.
And the pressure of hydraulic oil system is about 100 bar.

Thank you,,,

 

The Device Summary should list the charge pressure for the accumulator. I have also sometimes seen it shown on the Hydraulic System Piping Schematic Drawing (P&ID).

The accumulator manufacturer's instructions should have been provided with the Service/Maintenance Manuals provided with the unit. If not, obtain the accumulator manufacturer's name and use your preferred Internet search engine to look for instructions or manuals for the accumulator.

The hydraulic system must be OFF when performing this procedure.

I have also seem small "stickers" affixed to the tops of accumulators with instructions about how to attach the charging hose/gauge assembly to the accumulator. One end of the hose (the one with the gauge) has a connector similar to a screw-on tire valve stem with a large knurled ring above it. The other end of the hose should have a connector which can be attached to a regulator on the nitrogen bottle. The regulator should have sufficient adjustment range to control the pressure in the accumulator bladder.

This is the part that most people fail at <b>BUT</b> the large knurled ring must be "backed off" before the valve-stem looking attachment is made to the top of the accumulator or the pressure in the accumulator will bleed off. The large knurled ring is <b>NOT</b> the means by which the accumulator hose/gauge assembly is screwed on to the accumulator. Once the valve-stem attachment is made, the the large knurled ring on the hose assembly above the valve-stem attachment can be turned to "open" the valve stem mechanism.

With the nitrogen bottle regulator fully backed off (at zero pressure setting), slowly open the nitrogen bottle main valve to the regulator. Then, slowly screw in the nitrogen regulator handle until the pressure gauge at the accumulator is at the required pressure. Then back off the regulator adjustment and close the nitrogen bottle's main valve.

Using the large knurled ring on the top of the accumulator connector, close the accumulator valve stem, then remove the accumulator hose from the accumulator connector.

That should do it.

There may be an isolation valve for the accumulator gauge; if so, you will need to use it accordingly.

Again, the part most people fail at is attaching the hose to the accumulator. Pay attention to the attachment mechanism; it's very important.

Best of luck; let us know how it turns out for you!

 

Mr. CSA, thank you very much for response.

But there is a question about the regulating of pressure inside the accumulator, as we have: nitrogen bottle (20 bar) and piston accumulator that need for 40 bar pressure (as P&ID manual).

Do we need a compressor to increase pressure of nitrogen before filling accumulator?

Thanks.

 

Kene,

You should be able to get a bottle of nitrogen filled to a higher pressure from your local vendor/distributor. I've commonly seen nitrogen bottles filled to approximately 100 barg in many parts of the world.

Failing that, then, yes; you will need to use some kind of compressor to increase the nitrogen pressure to the necessary pressure in the accumulator.

 

Can anybody tell me what should be the nitrogen Pressure in Accumulator for Frame-6 machine. we have no reference base data for the same & even it is nowhere mentioned in P& ID diagram of GT.

Recently, we have measured for One (out of 3 GTs) for reference, & It is found 20bars.

 

MJ,

You should be able to find the pressure listed on the Device Summary for the machine. The hydraulic accumulator, AH-1, should be listed in the Device Summary near the very front of the document.

If the turbine was provided by GE, you should be able to find the Device Summary document in Vol. III of the operation and service manuals provided with the unit, in the same tab where the P&IDs are located.

The Device Summary document lists the setpoints for most of the pressure switches and temperature switches and similar devices used on the turbine and auxiliaries.

My recollection is that the bladder pressure should be approximately 1/2 to 2/3 of the normal Hydraulic system pressure, so if that's 1500 psig, then the pressure in the accumulator bladder when there is NO hydraulic pressure should be approximately 750-1000 psig.

Please be sure to use the accumulator charging hose correctly; many sites have inadvertently discharged the bladder while trying to charge it. There are usually instructions on the top of the accumulator assembly, or on the accumulator documentation in the operation and service manual.

 

I am not familiar with GT's hydraulics. I can comment on ST's which should have similar design characteristics.

the accumulator MUST be "precharged" with nitrogen when it is not in service. that is no hydraulic pressure applied. most accumulators I have seen have isolation and fluid drain so the precharge can be checked while hydraulics are in service. IF you check the gas side pressure of an accumulator in service, the gas pressure should be same as hydraulic. If not, then the accumulator is inoperative. you CANNOT add or vent gas at this time as the "volume" of gas is the critical value and can only be determined by knowing the ratio of gas/fluid.

I have seen two designs of gas fill "Scrader valves". the ones used <5KPSI are nearly idinical to those on tires. the filling cap is screwed on and a stem depressing plunger screwed in to allow accumulator gas to enter or exit.

the >5KPSI is slightly different in that it has the thumb nut that opens and closed for gas addition or venting.

the "normal" design of an accumulator is that it is precharged to ~ half of the normal hydraulic pressure. this can vary based upon the intended use of the accumulator. for example the older LSTG EHC system operated about 1600 psig and the accumulators that provided system flow during transients were precharged to 1000 psig. the low hydraulic supply trip was at 1100 psig so on the loss of pumps, the accumulators fluid would be very near empty just at unit trip. the accumulators that provided jet supply to the servo valves were precharged to 800 psig.

 

Thanks CSA,

We have checked in Device Summery & PID drawings, But the pre-charged pressure reading was not available. This was might be due to as our machine supplied in about 25 years back.

By the way we have checked the pressure for another GT (Frame-6), it is found 28.1 Bar.

 

MJ,

You can't go wrong with JFB's advice and procedure. We are basically in agreement: the charge pressure <i>when there's NO hydraulic pressure</i> should be approximately one half of rated system hydraulic pressure. I've seen as high as two-thirds of rated hydraulic system pressure(which is just one-sixth higher than one-half of rated hydraulic system pressure ).

Again, there are excellent recommendations in JFB's response. Just be sure you're using the charging hose and connector(s) properly and you should be fine.

 

Is this accumulator a piston or bladder design?

even with both designs, If they have not be properly charged while in service, there is a VERY high chance they are damaged. If you don't inspect, then at least verify there is no fluid on the gas side.

As for bottle pressure, the industrial nitrogen I have seen were over 300bar when full.