Accumulator charging help

[ParkerFly]

I'm trying to get my head around hydraulic accumulators and am having some trouble. I need to add one to a piece of equipment for storage (5 gallon bladder style) that will be used to quickly extend two cylinders. Here's where I'm not sure what to do. After the cylinders are extended, how does the fluid get back to the accumulator? I could run the accumulator at low enough pressure so that the cylinders could push it back in when I retract them, but I'd have to hold a valve open until it gets there and then close it before I let off of retracting the cylinders. Seems like a lot to do when I've got my hands full already before adding all this.
I also thought about installing another valve to dump the fluid off the cylinders and another one to recharge the accumulator, but I won't be near it to monitor my pressure and know when its full, plus still having to control another valve to hold the fluid in.
Hopefully this isn't too confusing, but can anybody help? I'm sure there's a simpler way of doing this than I'm coming up with. Thanks,

Justin

 

[J_J]

I believe accumulators are charged with fluid through a check valve to about half the capacity of the accumulator.

There should be a check valve to keep the fluid ready for use, and also, an unloader to stop charging when full.

The accumulators are used to smooth out hyd pulses, and for an instant supply of fluid under pressure for things like releasing brakes on hyd wheel motors, etc.

Sometimes they have a manual pump to pump up the pressure.

 

[oldnslo]

Justin,
Is this for emergency back-up power or constant use system? Different applications/uses require different valving to incorporate the accumulator.


Emergency back-up power: These are sized for x-number of functions with no external power. Then when the power is turned back on a pump refills them for the next power outage.

Constant use: We need more information on what sequence of operation you are trying to obtain.

 

[Zebrafive]

I am thinking similar to JJ. You need a line from your pump with a check valve to fill the accumulator, with valve to shut when full. Could this be a pilot operated valve that does not shut until a certain pressure is reached?

For output to the cylinders you could have a pilot operated valve that opens when it has pilot pressure from the control valve to the cylinder to extend.

 

[ParkerFly]

When it is used it will be every couple of minutes or so for an extended period. There will always be a couple of minutes in between uses when it is being used, so there's time to recharge it. My only concern is the hydraulics are doing other stuff during those couple of minutes, so can they still do the other functions and get it charged?
All my current valving is electric, so anything I add I would like it to be electric also. I have a port on my current valve that isn't being used, and had thought about using that port to charge the accumulator. I know the size I'll need is 5 gallon and it will discharge a little less than one gallon each time its used.

 

[wdchyd]

Your accumulator will have to be plumbed between the pump and control valves (closed center)....the cyls retracting will send exhaust flow back to tank, not back to accumulator

If you have a positive displacement pump then is the pump running all the time or on/off with elec power? with elec pump you may need a pressure switch to toggle the pump on and off to sustain pressure in accum

or You may need to add an unloading valve/circuit to refresh the accum circuit if it's positive disp pump constantly running....

or a variable displacement pump with pressure controls to cut-off when max pressure is reached during idle time

Accum circuits are great but you have to properly plumb it along with a means to discharge the pressure in the accum when shutting down the machine

Just something to consider

 

[CJONE]

Accumulators are charged with nitrogen usually to 50% of rated pressure. Most systems that use them are closed or pressureized [sp] with a comp piston pump or are used as pulsation dampers. If you are feeding a seperate circuit with the acc. then it can be used with a check and filled with a open system when it is used to actuate the other functions but there are ALOT of variables that have to be considered. Need alot more info. And you are correct a 5 gallon accumulator will give 25-30% at 1500psi from a 3000psi drawdown. CJ

 

[EE_Bota]

Most times, the accumulator is down stream of the pump, and a check makes it so the fluid cannot back flow to the pump when the pump is off. It is good practice to have an easy way to dump the accumulator to tank to make it possible to get rid of stored pressure so system maintenance can be accomplished.

Charging the accumulator to half the expected system pressure is a good approach most times. But expanding gas cools, so sometimes if you go up to half pressure in one go, the gas was so cold, the pressure will increase later in use as the temperature rises.

I have done more complicated approaches such as sequence valves, etc, but I like the approach of keeping them much like what a water pressure tank does in a well system.

 

[Redneck in training]

When it is used it will be every couple of minutes or so for an extended period. There will always be a couple of minutes in between uses when it is being used, so there's time to recharge it. My only concern is the hydraulics are doing other stuff during those couple of minutes, so can they still do the other functions and get it charged?
All my current valving is electric, so anything I add I would like it to be electric also. I have a port on my current valve that isn't being used, and had thought about using that port to charge the accumulator. I know the size I'll need is 5 gallon and it will discharge a little less than one gallon each time its used.

That is quite easy to solve. You need two check valves and orifice or adjustable valve with parallel check valve . One CV is installed upstream of the place where the accumulator is T in. One CV is placed in the line upstream of the accumulator such a way that it allows discharging the accumulator at high rate. The parallel orifice then limits the flow during recharging. In example the CV will allow the accumulator discharge in seconds while the orifice will allow it to recharge in minutes. You also need to plumb in the accumulator close to the cylinders and/or use rather large piping to achieve the speed you require.

 

[J_J]

Here is an accumulator charger valve.

Accumulator charging valve