Lubricator Drives

[GWRdriver]

I am presently re-working an unusual continuous-feed mechanical lubricator design (by D. Broughton published in ME 3 March 1972) and my question is about the shaft drive mechanism.

I enjoy making ratchet wheels (seriously - I do) but the pawls and springs are a royal pain and I know that nowadays the one-way or roller clutch (what used to be known in the US as a "Sprague" clutch) is being used for lubricator drives. I see from the specs for a ready-made British lubricator that two roller clutches are used for their drive. Could someone enlighten me on why two clutches would be needed, or better, . . . aside from having continuous shaft rotation? Is there a need for mechanical redundancy?

BTW this is an ingenious design, and no more complex than a any other pump design, and I've often wondered why it never appeared on a project nor was mentioned in ME again.

[ron]

Hi Harry
The proprietary one I have has two clutches, but it looks as if the second one is only really acting as a bearing to support the shaft. It looks as if it would work fine with one roller clutch and a bearing but it's probably easier for the maker just to use two roller clutches
Ron

[greasemonkey]

Hi Harry
The two roller clutches work in exactly the same way as the the two pawls on the ratchet wheel. The two bearings are inserted into the housings to work against each other. The first applys the drive to the horizontal shaft connected to the cam acting on the cylinder during the forward stroke, the second freewheels during this stroke but acts as a brake forcing the first bearing to release the shaft for the return stroke when it all starts again. If you didnt have the second bearing the first drop of spilt steam oil would create a viscous coupling between the shaft and first bearing that would only make the shaft rock and not rotate continuosly. Try it with a ratchet and pawl pump by disconnecting the return pawl to see the same effect. As usual it is easier to demonstrate than describe.

Andy

[GWRdriver]

Thanks all, . . . 2 pawls, 2 clutches, for the same reason, it's abundantly clear to me now.

[ron]

Andy
The proprietary one I have has both clutches the same way, if they were acting against each other the shaft wouldn't turn, they are one way clutches??
Ron

[havoc]

The proprietary one I have has both clutches the same way

Are they acting on the same components? I mean, I would expect one of them will have to work between the arm and the pump axle, the other against a static piece (chassis) and pump axle.

[greasemonkey]

HI Ron
Have a look at the diagram on the Polly site here
www.pollymodelengineering.co.uk/global/technical-notes/roller-clutches.asp
Think of the clutches taking the place of the ratchets in a traditional pump.

Andy

[ron]

Cheers Andy
I get it now [doh!] kindly disregard my previous posts, they are rubbish

Ron

[Tel]

The late, great Ron Allaway used to make lubricator drives with only one roller clutch - the function of the second one was performed by a close wound spring, just two turns or so, a tightish fit on the shaft, with a 'leg' fixed to a convienient point.

[GWRdriver]

TEL,
Hmm . . . . interesting idea, because I have an over hand problem to deal with. The width of a 1/8" ID roller clutch is .250" typically, add to that the thickness of the arm and collar, and maybe a washer or two and I have a drive appendage that will protrude at least .650" from the tank wall which I find to be objectionable. I want to devise some means of reducing that distance and the return spring might be one solution, along with housing one clutch within the tank.

[Tel]

The spring idea works quite well Harry, It is used a lot in typewriters & old type office machinery. Ron was, in his later years, a typwriter repairer - which is no doubt where he got the idea. You need to set it up so the forward motion of the shaft tries to 'unwind' the spring, then when the shaft tries to run back, on the back stroke, the spring tries to wind tighter & grips the shaft.

[Tel]

..... but if you go with two roller clutches, the second (standing) one can be housed inside the tank, rather than outside, or even over on the other side of the tank - they don't HAVE to be side by side

[greasemonkey]

HI Tel
Nice idea might give that a try inside a scale outline lubricator.

Andy

[Tel]

Can't see why not.

Harry, I've bumped up the 'Mechanical Lubricator' thread - that multipoint I posted the pics of has roller clutch drive

[steamjohn248]

We've built quite a fewof the Ewins lubricators now and would not consider any other type. We only use one clutch on the actuating arm, the head of the piston/yoke bears against a piece of springy copper which stops the thing going back the other way on the return stroke of the arm. Another way is to apply friction to the shaft itself, does'nt need much, the ball valve in the bottom of the cylinder stops the piston being lifted by steam pressure during the return stroke and there is no tendency for the roller clutch itself to pull the shaft round the wrong way.
These pages have been pointed up before but in case anyone reading this has missed them
ME 22 july Page 89 and ME 13 June 2003 both show very clear drawings though both show two clutches, added cost, not required.

Steamjohn

[chris vine]

Hi Harry,

Some people recommend hardening a silver steel shaft for roller clutches to work on.

Also there is some lost movement with these things. Although there is apparently none at all, there is still some resilience in the system because steel is springy, and there will be a little bit of wind up before the pump moves. This is fine as long as you have enough movement.....

Chris.

[GWRdriver]

Chris,
I planned to use hardened and ground shafting. Many years ago, in a former life, I was in the printing business and our rotary presses were Heidelbergs, magnificent machines, and each of them had a number roller clutches which behaved as you say, there was some motion lost in each reciprocation.

[markt]

The lubricator i bought from Steamfittings had two clutches and a hardened shaft. One clutch is pressed in the drive arm and the other is in the housing of the body. It came as a kit that i assembled using the isometric drawing provided and the clutches go the same way round.There is an exploded diagram in their Ebay shop which shows the assembly and the clutch rotation but as its a small picture it isn't as clear as the drawing i received.

[Tel]

yep, the second (standing) clutch is only to stop the shaft running back on the return stroke - there are a number of ways you can achieve that