I need help in a radial piston motor curcit.

Motor is connected with diraction control valve
A and B closed and P to T in nuturel position .

Would you recomend vaccume freewheeling, Motor manufacturer do so.


This type of freewheeling is possible only with a motor spool valve witch has P,A and B ports connected to T in neutral .Is it right

I do not want motor spool becouse i want maximum pressure at port T there is another DCV connected to it in serial.

How can i solve this problem. can I connect A to B in neutral.this is not vaccume freewheeling but it can be a option.as far as i know, it can be a option but in speeds lower then max.int.

Everytime DCV goes in a neutral freewheeling is very much requierd .
This is a open loop,everyone should keep it as simple as possible.

Hi Tony,
Most radial Piston Morors that are capable of FreeWheeling
(for high speed towing for example), The FreeWheeling achieved
by exposing motor casing to 2-3 Bar and A & B to Tank. The
internal pressure causes the pistons to disconnect from the
the counter part. Any other solution will cause cavitation
at higher speeds then manufacturer specification.

Motor spool valve? I guess you are referring to power beyond valves which is better than two valves in series. The best valve to use for motor(for freewheeling/ pulling horizontal) is probably a "float type"(a/b to t, p blocked/power beyond), but if there is a brake system, the brake pilot is external. Another thing is an anti-cavitation check valve must be installed.

A system using two dcv in series(tandem) is weak, but can be used for low pressure application wherein the first valve's tank port is strong enough to withstand the required pressure capacity of the second valve in series.

I guess you are concerned with your pump(fix displacement) that it might build up pressure when P is blocked, that's why you want to use an open/ tandem centered valves. There are valves(danfoss, rexroth, vickers, etc) that can be used for multiple actuator systems and looks like P blocked, but is equipped with shuttle valves(built- in) that unloads the pump at low pressure even if the P is blocked. The process is just venting the built-in relief valve at neutral position of the valves using the shuttle valves.

Nahum, I haven't heard about the motor case drain being pressurized. I was made to believe that all motor or pump case drain should possibly be unrestricted(zero pressure if possible to tank)... Enlighten me...

If a proper circuitry is used(with a return check valve, maybe 3 to 5 psi) and the case drains are normally ported to return separately, with anti cavitation check the motor can be easily freewheeled.

please take a look at this(atteched file) and suggest .

it looks like there will be no cavitation if A is connected to B in neutral with out any add on chack valve.

for me it is the best idea.
please give your input if you can read and understand this catlouge.

freewheeling is not requierd in towing there is a detachable gear for towing in case of breakdown. there is no need of hydraulic breaking also.

gm.pdf (226 KB, 95 downloads)

Ive never used this motor in an application that took advantage of 'vaccuum freewheeling' Will the transition of allowing the pistons to drain, and refill under low speed and low pressure conditions be a problem for you?

Even though the literature does not sugest it, just connecting a to b will result in some cavitation as oil will be lost out of this 'closed loop' into the case. But according to the literature some cavitation is acceptable.

It all depends on your exact application, but generally my prefference is to connect a and b to t (motor spool or float spool they're the same thing) and provide some boost pressure through a backpressure inducing check valve (obviously requres some external 'flow source' between the tank port of the valve and the back pressure inducing check valve.

This SAI motor cannot be freewheeled by using case pressure to keep the pistons retracted, or extended in this case, as there is a ring around the piston shoes holding them against the cam on the shaft.

A motor like a poclain can use case pressure to hold the pistons retracted into the barrel so they do not contact the cam ring, however this motor doesn't use a cam ring, it uses a cam shaft.

this freewhilling just needed for a few moments in a vahicle when it goes down hill.the speed will not be more then max.intr.
a motor wich can run for hours in vaccume, can not run a few seconds with oil + vaccume and no pressure at A and B.
is it allright.

According to the catalog you should be alright. If the pressure induced from the downsream function is less than 2500 psi, you could then use an all ports open or open center valve but in this case include a backpressure check valve downstream as in example A.

Example C looks like the easiest solution except for finding a spool with a nuetral funtion of A connected to B and P connected to T. You could add a seperate shunting valve to connect A to B and use a standard tandem center I suppose.

What type of valve are you planning on using? I get the feeling you are using a subplate type solonoid valve? Just on/off or proportonial?

it is a littel confusing(my curcit),let me explain it to you step by step,
I want two motors runnig with only one fixed displacement pump .
i am using two tendem center valves ,hand lever oprated in series.
only one motor will be on at a time.
one of the motor is for vahicle drive.witch has to be freewheeled when it is going down hill.
------------------------------------------------------------------------------------------------
the second senario is DCV A neutral
DCV B on

DCV C on
motor A running privided there is enough pressure in the system (with depands on load on motor B)

in both cases system should run smoothly.
the spools i am using--
in DCV A--- P to T and A to B in neutral.
in DCV B--- P to T and A and B blocked.
in DCV C--- all ports blocked in neutral.

theare is a on off valve 'X'.

freewheeling only required in a situation when pump running only motor A with DCV A .

Mr. Doug .do not worry there are pressure relief as and where needed in system.
Tony and Rock are both my id,s

This message has been edited. Last edited by: rock,

Just be sure whichever model of control valve you use allows high back pressure on t port, which you probably won't find, so you'll need a series spool with power beyoned port and A to B connected in nuetral. If you get a valve with power beyoned, it will have to have a series spool, or you will loose your flow through the tank port. Have you found a valve that will work yet?

there are valves available for series aplications.

a danison dealer says 3D 06 35 407 03 04 50 b1
can handel pressure at T port.I somehow cannot find any catalouge of danison on net.

http://www.denisonhydraulics.com/Products.html

the catalouge download link is not working yet.
anyhow i'll get these valves.
i am going to fit all componets in next few days.

This message has been edited. Last edited by: rock,