1928 Douglas EW hand oilpump

[patrickhowell]

I have recently stripped this pump to replace the 3 worn-out leather washers. Prior to that, the pump seemed to be working normally, as far as I can tell, with no previous experience on type. Initially, what appears to be an over-long spring ( it is  bulging out sideways) was being forced down without any delay, and without delivering any oil. I then removed the pump to check all was assembled according to the technical drawing, which it was, but on attempted reassembly onto the tank,  the plunger will not go more than about 4 or 5 cm. before refusing to go further. Any ideas, folks?

[patrickhowell]

Here is a photo of the pump. The spring is 5.75" free length as opposed to the book figure of 5.5", and there are 16 coils rather than 14.

[cardan]

That's a pretty massive spring for an oil pump! At least it looks that way... If the pump is out of the bike, as in the photo, can you hold the screw-in bit and pull the plunger up until the spring is coil bound? If not, the spring is probably too strong.

Leon

[cardan]

Sorry - is the problem putting the plunger into its tube? Don't forget this thing is just like a bicycle pump. If there is no outlet for air/oil trapped below, the plunger won't go in.

Leon

[patrickhowell]

The spring is about twice as thick as the book figure, so I subscribe to the idea that it is too strong. I have tried pushing the plunger in without the spring, but it meets with what feels like hydraulic pressure, and won't go all the way down. What do you think could be preventing it? The top hole in the tank tube looks to be clear. Thanks

[oily bloke]

Hi,
You have a clacket valve in the boss at the outside base of the oil tank. This may be blocked.
I would remove the aforementioned boss and drain the oil tank. That way you can prove hydraulic lock or not and you will be able to see up the pipe to determine where/if it is hanging up. My pump tube had ridged where the pump was left for yonks before restoration. I simply honed the ridge edges off and it works fine.
The spring is definitely way too strong. It only needs to gently overcome the oil and clacket valve resistance and apply a tiny amount of pressure.
It should be a simple fix.
Andy

[patrickhowell]

Can anyone give the correct spring length for the hand oilpump? My drawing gives 5.5" whereas the distance between the inside of the threaded tank top fitting and the base of the brass plunger/ piston is 3 7/8"? Also confirm that the spring should be parallel for its whole length?

[eddie]

Patrick,
           It is preferable to have a longer, weaker spring rather than a shorter, stronger spring to push the plunger down. The actual pressure is the product of the spring rate and the amount it is compressed. If the fitted spring has been compressed by, say, 1½" - then raising the plunger by a further 1½" will exert double the pressure on the oil in the pump. If a shorter spring that is only compressed ¼" is fitted, then raising the plunger 1½" will cause the pressure to rise 7 fold - thus making it almost impossible to sensibly regulate the flow over the full stroke of the pump. Having the longer spring will obviously increase the shut height of the spring - hence the fitting of the spacer tube on the pump spindle to restrict the stroke of the pump.
  Regards,
                Eddie.

[patrickhowell]

Thanks, Eddie, but what should the spring length be?

[eddie]

Patrick,
            I have just measured the spring from my 2¾. It is made of 70 thou dia wire, is 5.25" long, and is .900" dia with the last coil on each end squeezed down to .800" dia., and has 14 full turns. Bearing in mind that this spring is now 102 years young, it has probably settled a little, so the original dimension of 5.5" is probably correct.
  Hope this helps,
     Regards,
                  Eddie.

[Chris]

Hi Patrick
I think the drawing that you are referring to was produced by me and based on the dimensions of the pump assembly of one of my 2.3/4 hp machines. I cannot remember which one. (I have CW, TS and SW models using these pumps.) I have just checked a spare oil pump spring that I have and that agrees very closely with the dimensions given by Eddie. I have another complete pump assembly destined to go into a current project which differs from the above in having a wire diameter of 0.8, has 16 coils an OD of 0.89" and an overall length of 5.3/4". This one also allows the spring to bow to one side when unrestrained similar to your illustration. Clearly there are minor differences over the years of production but they all seem to work OK. Chris.

[patrickhowell]

OK, thanks Chris and Eddie, I think I will stick with the drawing. I assume the spring is parallel along its whole length?