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Valve Type for controlling a Hydraulic Ram

Valve Type for controlling a Hydraulic Ram

Valve Type for controlling a Hydraulic Ram

(OP)
Good day all

This is not my specialty (Hydraulics) and I am finding it very challenging.

What I am trying to do is to pressurize a hydraulic cylinder in the pull direction (ram is always under tension) at a very slow speed from a electric powerpac . I need to control the speed and the max pressure which has not been determined as yet so that along with the flow rate will need to be adjustable . If i was to do it all with separate valves this is how it would go . first a inline check valve , next a adjustable throttle valve , next a adjustable pressure relief valve to the tank , then a 12v dc controlled pressure relief valve hosed to the tank. My question is can I get a manifold block with any of these components incorporated into one unit to simplify installation.

Any help would be appreciated

Regards John.

RE: Valve Type for controlling a Hydraulic Ram

Have you selected your pump yet? A pressure compensated variable displacement pump does everything you need without any additional valving.

RE: Valve Type for controlling a Hydraulic Ram

(OP)
Thanks for the reply's

Yes I already have the power pack installed its a 12v 1600 watt unit. It is also used in the system to power two reversible winches . This is it

https://www.princessauto.com/file/general/8541666_...

I will be taking the power off the bottom of the manifold block which I have mounted separately to power these two rams. I was thinking of using a poppet valve like this https://www.hydraforce.com/products/valves/solenoi... and when powered it would dump the pressure into the tank instead of just back to the pump side so it would have to have a 3 way block .

Regards John



RE: Valve Type for controlling a Hydraulic Ram

That is a fixed-displacement (although with two possible choices) gear pump.

Does the required speed of your cylinder motion coincide with the displacement of the pump (in either the high-volume-low-pressure regime, or the low-volume-high-pressure regime)?

Do you need "precision" motion control? (difficult to achieve with hydraulics in general)

Hydraulics with a fixed-displacement pump want to be "bang-bang". Either moving full speed one direction with all pumped fluid directed into one side of the cylinder and let the pressure float with whatever it wants to be in order to push the load, or stopped with the pumped fluid being bypassed to tank at minimal back pressure and the fluid in the cylinders trapped by closed-off valve ports, or moving the other direction full speed. They're unhappy with trying to modulate the flow or trying to split it partially bypassed and partially applying load. Possible, yes - but unhappy.

IMO wrong pump for the job. Should really be a variable-displacement pressure-compensated pump with an adjustable pressure setting. There are a multitude of control strategies for the displacement control.

'Course, the right pump is going to cost a lot more than that one ... (C$400-ish for a new one)

You may want to check the spec sheet at Princess Auto. There's a duty-cycle limitation, which isn't very long. One of the bad things about fixed-displacement pumps with a pressure regulator, is that they're really good at converting full motor and pump load into lots of heat and noise, and not much work.

RE: Valve Type for controlling a Hydraulic Ram

I'm thinking, what needs to be done here, is to put your control valve downstream of the cylinder kind of like a diesel fuel injector. A valve down stream would close to divert flow through a needle valve to control the extension speed. A regulator between the needle valve and cylinder with a return to tank would control max force. In order to actuate two cylinders independently, a selector valve upstream of the cylinder would divert flow to one cylinder or the other. A check valve on each cylinder outlet would allow them to be combined so each doesn't require a needle valve and regulator.

RE: Valve Type for controlling a Hydraulic Ram

This is probably an ideal pump for your application, a Metaris MHPVB5. It's 0.64 in^3/rev which should get you down into the ~ 2 horsepower range. Metaris makes cheap knock-offs of the brand names.

RE: Valve Type for controlling a Hydraulic Ram

Quote:


What I am trying to do is to pressurize a hydraulic cylinder in the pull direction (ram is always under tension) at a very slow speed from a electric powerpac .
So if the pressure goes away the rod will be pulled out?
If not how do you get the rod extended?

Quote:


I need to control the speed and the max pressure which has not been determined as yet so that along with the flow rate will need to be adjustable .
What are you really trying to do? Pulling requires force. That depends on pressure AND area. Do you know the pressure on the cap or blind side of the piston?
If the cap or blind side is vented to the tank then no problem. If not the pulling force will be
Force = Pressure_rod_side*area_rod_side-pressure_cap_side*area_cap_side;

Quote:


If i was to do it all with separate valves this is how it would go . first a inline check valve , next a adjustable throttle valve , next a adjustable pressure relief valve to the tank , then a 12v dc controlled pressure relief valve hosed to the tank.
This assumes the pressure on the cap side is 0 psia.
Relief valves are not control vales. They are safety valves.
Controlling speed will be a problem without position or speed feedback.


Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com
http://forum.deltamotion.com/
IFPE Hall of Fame Member

RE: Valve Type for controlling a Hydraulic Ram

(OP)
This is what I am moving

https://www.navtechydraulics.com/vangs/

They are charged with nitrogen as the reverse force and holds up the boom.

As for duty cycle on the pump the most it will run is one minute .

I figure in order of operation the pump would first see an adjustable pressure relief valve then a check check next there would be a tee there that has a poppet valve going back the tank (for releasing pressure) then the last thing would be a adjustable needle valve (for very slow movement) then the cylinder .

What do you think ?

Thanks for all the help guys

RE: Valve Type for controlling a Hydraulic Ram

That's a picture of the cylinder. What about a picture of what you are actually trying to do with that cylinder?

Probably someone (maybe even myself) has experience with trying to move something similar to what you're trying to do?

RE: Valve Type for controlling a Hydraulic Ram

(OP)
Yes sorry , that’s the right application . Forgot you guys are not all sailors.
There is always a compression force on the cylinder. It uses a nitrogen charge inside the cylinder to counteract the compression and hold up the load . When pressurized with hydraulic pressure the cylinder is pulled down against the nitrogen counter force and moves the boom downward .

Regards John

RE: Valve Type for controlling a Hydraulic Ram

J Tully, the reason I suggest putting all control valves between cylinder and tank is that the cylinder itself will act as a bit of an accumulator when the system is operated. This will eliminate some of the jerking associated with the bang bang operating of fixed displacement systems.

If you put the reliefs and needle valves before there will be a large shock as pressure instantly builds relief. It will also always run under relief when the isn't moving. If you put the controls downstream there will be minimal loss until the system is moving or has stalled.

I'll try to draw it shortly.

RE: Valve Type for controlling a Hydraulic Ram

Pick a pump that is small enough that its full displacement moves the cylinder at the rate that you want it to move. If you use that dual-displacement pump and are able to control which mode it is in, you can have a fast and slow speed. Then you need only a three-position center-open (pump shorted to tank, A port blocked, B port blocked) directional valve and NO flow controls, and the pump will not be operating on the pressure regulator.

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