(reveiw) Hydraulic System with tandem center solinoid for control

[Talo]

hi i am fairly new to the hydraulic business and need to create a hydraulic lift that has warm up loop that also raises the lift at the speed i choose based on the power given to the pump. and lowers slowly with a regulator.


i made a schematic of the way i think it is supposed to be done.

here's the visio project in office 2007

http://files.engineering.com/getfil...8-a70e-2f9c8249e12a&file=Hydraulic_System.vsd

also attached is the image of the same schematic.

 

[hydromech]

Yes thats just about it...

Although your diagram shows the pump sucking oil out of the electric motor. I am pretty sure that wont work...;-)

The directional valve and the flow controls would be mounted as a stack on top of a single station manifold.

The CBV would be directly mounted on the port of the cylinder to reduce the risk of pipe rupture.

Adrian

 

[Talo]

ya i was looking into that cause i wanted all the valves to be on subplates to reduce connections. and i wanted to have all managmnent devices in one spot.

 

[Talo]

i have a quick question. if i use a counterbalance valve as a subplate it would be in "A" and out "A"?

or in "A" and out "B".
(

http://www.imav.com/EN/0201/IZ-530-402-00.htm)

my guess is that i need it to be in A and return A.
(

http://www.imav.com/EN/0201/IZ-530-450-00.htm)

remember this is if i connect it as a subplate on the directional valve..
.......


also if a use a subplate for the directional valves
does the one for the bottom port of the cylinder need to be faceing in that of "example A" or in "example C"?
this also goes for the top port of the cylinder, would it be connected as in "example C"?


See attached file for example directions.

 

[budt]

As a Counter Balance you need to specify it as "Out of the port you have connected to the side of the cylinder you are keeping from running away."

In other words if the cylinder is mounted Rod Down and the Load is pulling against the Rod End and the Rod End Port is connected to "B" Port on the Directional Control, you would ask for a Counter Balance Valve specified as Out of "B" port.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[budt]

BTW never put the Counter Balance at the Manifold if there is a Hose in the line oing to the cylinder. If that ose fails for any reason and the cylinder is in the air there will be a High Velocity Stream of Oil Shooting Across the Plant and a VERY LOUD NOISE when the CYLINDER BOTTOMS, PLUS IF THERE IS AN OPERATOR INVOLVED THEY COULD BE MISSING PARTS AT LEAST AND MAYBE WORSE.

I always put the Counter Balance Valve on the Cylinder Port with a 4-Bolt Flage mounting since a pipe nipple is subject to catastrophic failure while it is less likely with (4) S.H.C.S.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[budt]

On top of that, IF THERE IS MUCH PLUMBING LENGTH AND SOME HOSE in the line back to the Manifold and Counter Balance valve you very possibly will have a a CHATTER in the HYDRAULICS that has a VERY ANNOYING SOUND but ALSO PLAYS HAVOC WITH PLUMBING NO MATTER HOW IT IS INSTALLED.

BEEN THER AND DONE THAT, Just once though in my training days in the College of Hard Knocks that most persons learn about Fluid Power design.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[Talo]

lets say that i use a solid pipe up to the directional valve, willit still be problematic?

 

[Talo]

just another thing i was looking into.
for the directional valve i need to know what direction the restrictor valve and one way valve on the top and bottom ports of the cylinder.


look at page 2 of 8 and tell me if i need model S or S2 (right hand side above the schematic)

here's the link

http://www.boschrexroth.com/country...ownloads/RA_27518_0203.pdf?searchQuery=27518)

 

[hydromech]

I need to catch up a bit...

With regard to the CBV, ports AV and BV go on the cylinder side. The check valve allows free flow into the cylinder, but flow coming out of the cylinder is forced through the main stage of the valve. Oil cannot get out of the cylinder until the valve is forced open and if oil cannot get out, the cylinder will not move.

It is ideal to install the CBV directly on the ports of the cylinder in order to reduce the risk of the cylinder running away if a hose or pipe was ruptured. If you have look at the cylinders on almost any excavator or aerial platform, you will see a block attached to the cylinder. That block will house the motion control valves. It is not always possible to do this so you need to guard or protect the pipes or hoses to reduce the risk.

It has been my experience that the valve is more at risk from being jammed open by debris in the oil than a pipe is of being crushed. It is really your call, a quick risk assesment will help you to decide. I would never install hoses between a cylinder and the motion control valves.

The decision between metering flow in or out has been discussed at great length in this forum before now.

In basic terms, if you meter flow out of a cylinder you will stop the cylinder from running away because, as I said before, if oil cannot get out the cylinder cannot move. BUT..the extra pressure drop created by slowing the oil is seen by the cylinder and in some applications that may cause a problem.

If you meter the flow in, the pressure drop is less but the cylinder can overrun the oil flow. It means that the load on the cylinder accelerates it and the oil flow can keep the cylinder full. There would be no real control of speed and the cylinder creates an internal vacuum, drawing in air and sometimes turning seals inside out.

I always meter out, other people will meter in. Some suppliers have valve that can be simply turned over to change them from meter in to meter out. You could try it both ways to see which gives you the best performance.

By the way, what made you go for that size of valve? What is flow rate, could you use a size 6 instead of size 10 valve?

Adrian

 

[Talo]

i originaly wanted to use a 1/2" pipe with a orb#8 connector because the setup had parts that were only designed for a D05 plate. and in my case a D05 plate had output to #8 orb ports.

the flow rate is around 2.5 to 3 gpm

 

[Talo]

sorry gpm is 2.89 exact

 

[hydtools]

Please use tube and tube fittings, not pipe and pipe fittings. You will have better success for leak-free connections.

Ted

 

[Talo]

i realze that but certain points need rigid pipe

 

[Talo]

ok according to this i need an H-spool directional valve correct? and then the counter balance valve would go through port a and come out port b?

also i don't think it will rupture cause im using steel piping to the cylinder which is in ground up to a small closet right beside the cylinder. so its not a long run. bout 5 ft pipe. with a o-ring on the end for leak protection. the rest of the system if possible will be rigid pipig if not then i will use normal tubing for the parts that are not ab;e to use rigid pipe.

 

[stroupaloop]

Real quick to clarify. I know I'm stepping in half way through the conversation, but a clarification on what hydtools is trying to say in regards to tubing and piping needs to be expressed.

Piping should typically never be used for your type of application with low flow, low pressure and small diameter. Typically piping is used for large water and gas-line practices, but causes some inherent issues with vibration and temperature. Additionally, pipe threads cannot tolerate vibration, shock or thermal stresses. Even when piping is utilized, they will typically weld the ends to reduce leakage effects in low pressure locations of the system. The piping will also typically introduce large amounts of contamination into your system due to the processing of the pipe.

Tubing is your better choice becuase it can easily be bent, flared and is rather ductile. Typically, for your low pressure system, you will want to use a flared connection, such as JIC, where the flare sits at 37 degrees and is readily available. You could also use something more leak resistant like a swage, which can be bought from Swagelok. The swage utilizes a two piece ferrel set to help lock the connections together.

The main difference between tubing and piping when seeing them side by side is their diameter rating. Piping runs on an inside diameter rating, where as tubing runs on an outside diameter rating. With tubing you need to be aware of the thickness becuase this will effect the pressure rating the tubing can withstand, likewise with piping when applicable. If you are using low flow such as 3 GPM and relatively low pressure, I'm not sure why -04 or -06 tubing can not be used, maybe -08 if there are a lot of resistive locations within your system.

Typically when sizing your tubing you want to have a target fluid velocity of around 7-20 ft/s on the pressure side. I'm not going to do the calculations for you, but I have faith you can calculate it out. This will ensure are general turbulent system, which will reduce other negative effects within your system.

Being that I am a big advocate of contamination cleanliness and you're working with underground operatino next to the dirt. Have you considered introducing a filter to increase system reliability?...

 

[Talo]

yes i have a filter in the design one mesh filter for the return and a oil filter (cellulose) for the outlet back into the system

 

[hydtools]

The mesh filter/strainer must be in the suction line to the pump. Either installed in the reservoir or inline to the pump.

The filter in the return line to the reservoir should have a flow rating of 2 to 3 times your system flow. You will have to decide the level of filtration you want to keep your system clean.

Ted

 

[Talo]

this i know allready thanks though.

but i still did't get an answer to my previous posts.
cause i noticed that manufacturers of logspliters for instance use rigid pipes for the top port of the cylinder, as well as CAT on their tracktors and excavators.

 

[hydtools]

CAT uses steel hydraulic tubing.

Ted

 

[Talo]

ya i know so im asking why can't i use steel pipe?