Controlling Motor Speed CAT IT28G Auxiliary Circuit

[ZacMech]

Hello, I'm a Mechanical intern and I have a (hopefully) simple question. The plant where I'm working uses a an auger to sample bulk material that we receive. The auger is powered by a hydraulic motor that is mounted on a frame, and the frame can be attached to the boom on the CAT loader. The loader's primary pump (a vane pump which connects to the main control valve) puts out 20gpm at ~1000psi at idle.

In order to get the correct sample size, we want to vary the speed of the motor(and thus the speed of the auger). We initially just used a needle valve to throttle the flow, but this resulted in too much heat build up in the system.

We then contacted a hydraulics consultant, who specified a DCV with pressure compensation, load sensing and a metered spool as well as all the additional components required to install this (shuttle valve, joystick, hose etc). He also suggested tying in to the steering pump so the lift and tilt functions could be used while sampling. Two things: first, the steering pump only puts out 13gpm at 1000psi, so this flow isn't high enough to get the motor speeds we want (without buying a new motor). Second, if it is not critical that the motor be at an exact speed all of the time (i.e. it can vary somewhat) do we even need the load sense?

An idea I had was to use a variable flow control valve (such as the FCR51-3/4 by Brand Hydraulic) and put it directly after the valve which controls the auxillary function on the loader. The controlled flow would go to the motor and the excess could be either routed back to tank, or on through the rest of the main control valve (this would allow control of the lift and tilt functions while sampling-although it would be slow if there isn't much flow going that way). It would also have to be ensured that the excess flow port is closed when the auxillary function (sampling) isn't being used or flow would divert through there (or a check valve could be installed on the excess flow line). Also, we would like to vary the flow from 20gpm down to about 10gpm, depending on the material being sampled.

I have included the system schematic (hopefully it shows up) and appreciate any insights, if this simple fix seems plausible it could save us a lot of money! Thanks again for any help and please let me know if there are any other details I can provide.

 

[hydtools]

Your idea will work. The FCR51 will bypass excess flow at the auger motor demand pressure. It has a relief valve built in, so be sure it is set to provide high enough max pressure to drive your auger at max load. Alternatively, get the flow control without the relief valve and just depend on the systems relief to protect the motor. There will still be a heat load, just not as much as using the needle valve scheme.

Using the needle valve to set flow causes excess flow to go through the system relief valve at whatever its setting is.

Ted

 

[budt]

The Q Q outlets from that Directional Control appear to be unused and it is controlled by an infinitely variable Joystick, CC DD Lever.

If so I would use one of its outlets and feather the output to any desred flow through Joystick manipulation. You could use a mechanical stop so the operators can't make the motor run too fast. That would make the least heat since excess flow wuld go to tank at load pressure.

You could even have reverse capability for the motor by connecting both motor ports to the Q Q outlets.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[ZacMech]

Thanks very much for the quick responses. This forum has been a really great way to learn about hydraulics, especially since I find it really interesting and would really like to get into the field after graduating.

Bud, that is actually how the motor is connected now. The Q-Q lines are either pressure or return lines depending on the position of the control valve (so the motor can run in forward or reverse, which we need it to be able to do). One thing about the feathering method is that it might not give the operators a very high level of control. The idea is to give them a set procedure for sampling different materials (i.e. for _____ material, set auger speed at ____). The lift/tilt functions are controlled with one joy stick, and the axillary is controlled by an independent joystick (which is spring return). The aux. joystick could possibly be converted to detent, which would make it easier for them to set in one place and not have to hold it in position manually. I was also thinking about ordering a speed sensor, which the motor manufacturer can provide, and running a line from the motor to a display in the cab. This would make the actual settings on the valves less crucial, since the operator could tune the speed from the speed sensor display. Thanks again for any comments or advise.

One other thing, did we agree that the DCV (although a well made piece of equipment) was not really necessary in this application?