Hydraulic Transmissions

[gilesengineer]

Hose & General in Horsham were the company who provided the valve (and incidentally the motor - off a conveyor).

from my website...written by my brother

"The new valve duly arrived, and didn’t look much for £160. It was very compact, and they had got all the functions into a single spool. The requirement stated to the manufacturer was for proportional speed control in both directions> after asking questions about the use, I was told that it needed to have what they called a “freewheeling spool”. This in effect connects the two ports on the motor together when the control is release, allowing oil to freewheel around the motor on overrun. The normal arrangement is to block both ports, which would cause the pump to run dry or “cavitate” on overrun – a very damaging condition for hydraulic systems. The whole unit was the size of a smallish cigar box with a single centre sprung control lever. I was enormously impressed.
The installation of the new valve and hoses (made up by Hose & General) produced a chassis that would theoretically propel itself and so plans were made to make it drivable."

Sorry not to give a part number - it may be they simply built it up from standard componants to this spec..

[bigt1677]

Dec 24, 2009 1:31:51 GMT Boulder Creek said:

Thanks Ian,

Yes we do have chandlers and boat places who sell hydraulic winches. Unfortunately they know little about the winches they sell and even less about the hydraulics that drive them. I used to work for a company who made boat winches and even they weren't much help. A local hydraulic supplier was less than interested in my project and said if I could come up with a brand and part number then they could most likely supply what I was after? If I was just after a valve to make a hydraulic ram go up and down or a thingy on the tractor to turn one way or the other then no problem. A miniature loco.... hhmmm....not sure if we can help you with that one???

Regards,
Dave.

Dave, try this site. Ok, it's not based in Oz but it is informative and may give you some clues as to types, sizes etc etc.

www.hydraulic-equipment-manufacturers.com/hydraulic-valve.html

Hope this helps

Trev

[Boulder Creek]

Thanks Guys,

I am going to try the local hydraulics suppliers again in the new year and ask them some more questions. I'll let you know how I go.

Regards,
Dave.

[jempc]

Dave,

It's worth putting some thought into how you plan to set up the hydraulics. If you've got a separate motor on each bogie and they're connected 'in parallel' to the pump / valve, then if one bogie loses traction, I believe that all the torque will be sent to that bogie, exacerbating the wheelslip.

The alternatives are to:

• connect them up 'in series'. I'm not sure how that works for efficiency as the first motor might use all the available power in the fluid leaving none for the second motor, but the potential traction issue has gone.
  
• use 2 pumps, one per motor. Things then get expensive as you'll probably need 2 valves as well.
  
• Accept that you're not going to make the most of the potential traction available from a Bo-Bo loco - you'll be no worse off than with a simple '0-4-0'
  

I hope this all makes sense, and I write as very much an armchair engineer at the moment, although with good intentions otherwise.

What do others think? Are my musings valid?

Jem

[havoc]

If you've got a separate motor on each bogie and they're connected 'in parallel' to the pump / valve, then if one bogie loses traction, I believe that all the torque will be sent to that bogie, exacerbating the wheelslip.

It would surprise me if they didn't have any kind of valve to solve that.

[gilesengineer]

I believe it would be correct to pipe them in 'series'. Indeed, if you were to pipe them in parallel, you would need double the flow rate for the same speed, and in the event of wheel slip, the non-slipping bogie would slow right down as the slipping one went faster (unless you had a fully dual circuit system). If the motors are in series, they are 'locked together', so you should get an equal performance from both bogies.

I suspect that a dual circuit system would have problems trying to get an exactly equal flow to both motors - and if you didn't, one bogie would always be idling after the other, and doing no work (assuming free-wheel spools - otherwise the wheels on one bogie would be turning at a different speed to the other bogie - not good...)

(I would point out that I am not a hydraulic engineer, but merely someone who has to deal with a variety of different technologies, like so many others on this site.)

[dscott]

As I see it, the pump is the easy part by using an old one from a power steering unit off a car that has been scrapped. The expensive bits are the motors and of course the valve which in fact is almost like the slide valve in a steam cylinder, forward's backward's and an outlet set at a pressure back to the oil tank, quite easy.

What we need is a small design of motor that fits near the wheels with a pulley and connections for two high pressure hoses.

David.

[steam4ian]

G'day David

I can see you have a number of projects on the go!

For motors you could use power steering pumps operating in reverse.

Another option is twin cylinder double acting oscillators; such motors were good enough for the Tower Bridge.

Regards
Ian

[Boulder Creek]

Thanks for the input guys,

I do intend to connect the motors in series. That way they will both run at the same speed. It also makes the valving much simpler. I'm still a little unsure about the size of hydraulic pump and motor required but I have run some ideas past a local hydraulics guy and he is looking into it for me.
I'm not sure that a power steering pump would do the job but it might be worth experimenting with. Has anyone ever tried one for this use?

Completely off topic but, the pipe for the tunnel will be going in the ground some time this week if all goes to plan. Keep an eye on the “Boulder Creek Tramway” website for new photos!

Dave.

www.smex.net.au/bouldercreek

[fostergp6nhp]

I very much doubt that a PAS pump would have the flow and/or pressure. In the off road scene it has been tried many times using a PAS(ZF) pump to drive hydraulic winches, the end result is usually low power and veeerrry slow rope speed on the winch.

[angleseyrailway]

Dave,

If you are still looking for all the parts no's for your proposed petrol hydraulic loco, l can send them by private message.

I have the same engine and purchased all that l needed some 2 yrs ago. The system was designed by an approved hydraulics company.

I intend to sell my loco design as it will work for 7 1/4, 10" and 10 1/4" gauges.

Hope this helps.

Daniel