ext/ret a cylinder without a DVC

Question

ext/ret a cylinder without a DVC

industrialsparky (Electrical)

(OP)

28 May 06 12:43

i have to extend and retract a cylinder (and i must be able to control it) with out the use of a DVC this can be done using 1, 2 or 4 componants. i was just wondering if someone could give me an opinion on whether or not the circuit i have come up with will work or if i am on the right track. i am not the best at hydraulics. (*note: a vertical cylinder may be used instead of the horizontal)
thanks

500psi system pressure (the pump has a relief valve already incorperated) goes to both ends of the cylinder (horizontal with no load on it). the blank end will have a T on it also going to a neelde valve which then goes to the tank.
when the needle valve is closed(no flow going though) the pressure will build up on both sides of the cyclinder. because of the area on the blank end, the fluid will be pushed out from the rod end and back to the blank end (causing regeneration). the cylider extends.
when the needle vavle is opened, the fluid on the blank end will travel back to tank and the pressure will build up on the rod end. this should cause the cylinder to retract.

budt (Industrial) · Answer 1 · 2006-05-28 13:13:04

Close but not there:

When you open the needle valve to tank what will keep pump flow from going to tank?

Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us

industrialsparky (Electrical) · Answer 2 · 2006-05-28 14:19:59

i was thinking the amount that you restrict the flow back to tank or how much you open the needle valve

hydromech (Mechanical) · Answer 3 · 2006-05-28 15:21:31

The pressure drop through the valve being equal to or more than the pressure required to move the unloaded cylinder, then yes the cylinder will move as you suggest.

In actual fact, the force required to break the seal contact with the bore of the cylinder will be more than the pressure drop through the valve.

The pump will put all of the oil on the floor!

budt (Industrial) · Answer 4 · 2006-05-28 16:42:06

The pressure that you get from restricting flow to tank will still be on both ends of the single rod end cylinder and we all know what happens when there is equal pressure on both ends of a single rod cylinder.

Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us

industrialsparky (Electrical) · Answer 5 · 2006-05-28 18:54:16

its a two to one cylinder so it would stay extended i guess. do you have any ideas? i have spent a few hrs trying to figure out something but so far thats the only one i thought would work
the componants i have are : sequence valve, reducing valve, 2 needle valves, 1 flow control valve and two check valves

budt (Industrial) · Answer 6 · 2006-05-28 20:35:54

Take the circuit you dreamed up and put a second needle valve in between the tee you have with the needle valve going to tank and the tee with the line from the rod end.

Closing the tee to tank and opening the other tee extends regeneration.

Oprning the tee to tank and closing the other one will power retract the cylinder.

With 4 needle valves you can make it double acting with full force both ways.

Heck of a class assignment. What is the class title.

Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us

industrialsparky (Electrical) · Answer 7 · 2006-05-28 21:07:17

oh okay i get it, thanks alot. its just like an intro to hydraulics course. were learning alot of metering in and out, regeneration, counter blance differece between pressure control and flow control valves and some other stuff. im not fully understanding the course though. it's a very fast paced class and im trying to catch up. then again i am an electrician :P
you have your own company?

budt (Industrial) · Answer 8 · 2006-05-28 22:00:43

Don't you find a lot of correlation between DC and Hydraulics? I took some basic electrical classes once and could relate a lot of DC electrics to fluid flow.

I teach a lot of the Apprentices at at several local plants. The Mechanics get 128 Hours of Basics and Trouble Shooting while Electrical's only get the 64 Hours of Basics.

Actually I find the electricians pick up on a lot of the theory faster than mechanics.

I am a 73 year young Semi-Retired ex Fluid Power salesman that still does the same thing I did while selling just getting paid by the hour instead of commission. Same customers but I don't have a boss fussing about sales dollars. The company is just a necessary thing to keep it legal.

Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us

industrialsparky (Electrical) · Answer 9 · 2006-05-29 13:00:11

yes there are alot of similarities in the theory but for me, applying the theory to a wiring diagram is much eaiser then to a hydraulic one. right now we really dont cover DC theory either. mainly Ac because that is the most common in the indusrty. i think we need a little more time in the class to really understand and maintain the knowlege.
sounds like you have a lot of fun doing your part time job. keep it up

one of my class mate actually got my circuit to work....only he has alot more tee's and hoses to create some restiction (roughly 200 psi)

thanks again for your help
amanda

budt (Industrial) · Answer 10 · 2006-05-29 15:48:20

A few things that might help an electrical person:

Pumps don't mke pressure only FLOW

Pressure only happens when there is resistance to flow

Hydraulics & Pneumatics (Fluid Power) defines Normally Closed (NC) as a blocked or no flow situation and Normally Open (NO) as a path for flow or a hole.

As you can see it is exactly reverse of electrical since electrical is defining the Contacts of a Switch. So, when I am discussing Fluid Power with electrical types I use Normally Passing and Normally Non-Passing to keep everyone on the same wave length.

Voltage is the same as Pressure (PSI) in Fluid Power and Current (amps) is equal to Flow (GPM)in Fluid Power.

Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us

industrialsparky (Electrical) · Answer 11 · 2006-05-31 11:53:57

thanks! yea we uses the terms normally passing and non passing becuase its too confusing the other way.
we also found another way to may the cylinder ext/ret with only one compnant... a pressure reducing valve. the only problem was, we had to lower our system pressure and do the demo quickly becuase technically we were blowing the seals on the drain. if we disconnected the drain hose the circuit wouldnt work.

budt (Industrial) · Answer 12 · 2006-05-31 12:12:51

Someone learned a lot or was just trying anything to figure out the Reducing Valve circuit. It's not one I would have thought of though I can see how it works.

Also with that circuit you could stop the cylinder any place in mid stroke. At least the one I think you used could do that.

Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us

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ext/ret a cylinder without a DVC