hydraulic circuit review ... again .... please

[xtal01]

So .... I took all your advice ... did a bunch more reading and came up with a revised hydraulic circuit.

Just a quick review .... I am building a simple lift. The main section of the lift is a recycled electric forklift. I have stripped the mast of everything except the main lift cylinder ... simple single acting ) gravity down. I am also using the pump/motor.

I have included a N.O. dump valve so I can start the unit "unloaded". I will also tie it into the e-stop circuit to ed-engergize the unit ( even if something unexpected like the contactor welding on ).

I have included a "load check" so the unit will not "drop" when the pump is coming up to pressure.

On the lowering side, I have included a N.C. valve so I can stop the unit if the e-stop is actuated ( it would take a while for the flow valve to slow then stop the unit).

I have also included flow control valve on the raise and lower circuits. I want to get rid of the "jerk" when starting and stopping the lift.

So, can you guys review it again and see how I did this time?

Thanks so much again ..... Mike

 

[hydtools]

You will get a 'jerk' as soon as you energize that bang-bang dump valve after the pump is running. The flow control will not change that.

Ted

 

[xtal01]

Hmmmm.... I was thinking I would start the pump with the dump valve open so the pump is unloaded (flow valve closed). I would then close the dump valve with the flow valve still closed ( dumping 100% of the flow via the EX port .... or near zero ... maybe have it set to a minimum flow of say 1 gpm) ..... then slowly increase the flow from zero to the max flow is around 8 gpm ...

I thought increasing the flow from 0 to 8 gmp will get rid of the bump. Same on the way down.

Am I correct?

Thanks ..... Mike

 

[hydtools]

If you always return the flow control to zero regulated flow, full bypass, when you stop the cylinder upward motion, then you do not need the dump valve. The full bypass setting of the flow control valve with provide the pump bypass function.

Ted

 

[xtal01]

I have been wondering about this!

I just don't have a good understanding of how the flow valve works.

From what I read .... and please correct me if I am wrong .. the CF and EX side of the valve somehow balance pressure ( or at least this is what I took from the literature ). So if the CF side is "taking" 2 gpm at 1000 psi then the EX side will flow 6 gpm at 1000 psi ( assuming a total flow of 8 gpm). I might be very wrong on this!

My thinking is that if I close the flow valve completely then does the EX side of the valve not build up "full pressure" ... or would closing the CF flow to zero put all the flow to EX with no pressure build up?

I guess the only other argument for the N.O. dump valve on the lift side is to instantly stop and ed-energize the system. I am actually planning to motorize these mechanical flow valves so they cycle from 0 to full(10) when starting the lift and then full to say 1 gmp just before landing ... then to zero after landing. It will take 5 seconds to take the flow valve from full to zero. The dump valve will be instant and the load check will hold the lift at its position.

I know this sounds a bit nuts but I can do this with a simple $50 linear actuator and three limit switches ... the mechanical flow valves are about $100.

A few years back I was asked (I do instrumentation / control panels for a living ... along with being a machinist) I was asked to get rid of the bounce in a lift .... it was a simple hydraulic lift standing up nuclear fuel bundles. I simply bought two proportional hydraulic valves, set up a few prox. switches and ran everything off a PLC.

It worked awesome! But I spend about $5K doing the job. I did a bit of searching .... the cheapest proportional valves I found were about $400 each with a $600 board to drive them. Say $500 in a cheap PLC, $500 for software .... I would estimate $2500 plus in parts ... then I need to program it.

Anyway, a lot of money for a "home" project. Maybe one day when I feel rich I will upgrade to this but for now I want a simple and safe lift.

Thanks so much again .... I truly appreciate all your comments and advice!

Mike

 

[hydtools]

Set to zero, cf flow will be zero and all flow will go out ex port at valve flow loss pressure.

http://www.brand-hyd.com/

Ted

 

[xtal01]

You read my mind ( my wife says it is a short story ) .....

I am planning on using a FC51 1/2" ... this should give me good flow control between 2 and 6 ( zero to 10 scale ).

My original idea was to have a true mechanical system. I was going to trip these flow valves with a linkage or cable. Started designing it ... nightmare. Without my full shop in operation, it would be very hard to set up correctly.

I then got the idea of a simple ( and cheap ... $50 ) linear actuator to pull and push this flow valve controlling the speed of the lift.

Limit switches are cheap ..... $2 each on ebay.

I realize again this may seem a bit odd but it is only for a "home" system .... not to be used by anyone but myself.

Thanks .... Mike

 

[kiwitom235]

Do you really need the check valve on the return/downward line? I dont think you need it.

 

[xtal01]

I was wondering about this ... I only put it to prevent any "back pressure" that may be generated then the fluid goes thought the filter would not feed back into the down / return circuit.

Maybe the pressure would be so little it would not be needed?

Thanks .... Mike

 

[kiwitom235]

Hi Mike,

How do you plan on lowering the lift? Will the hydraulic pump still be running, or switched off?

If it is off, and you are just dumping the cylinder to tank, then you don't need the check valve anyway....

 

[xtal01]

Awesome ... thanks. Yes I do plan for the motor to be running only when lifting. I will shut it off when I hit the upper limit switch.

Mike