Double acting question

[Julian]

Hi,

I am most way through building a double acting oscillator (wobbler) and am at the point of drilling the steam ports.

Is there a relationship between the cylinder capacity and the size of the steam ports? Is there a formula or is it guesswork until it works properly?

My cylinder is 20mm bore and 36mm stroke with a 10mm thick piston giving a capacity each end of 2.6cc so what size steam port would anyone suggest? Swept volume is 2cc as 3mm of travel is for clearance but still needs to be filled with air.

Thanks

Julian

 

[Julian]

Hi,

Correction to the above post....The cylinder is 46mm long with a 10mm thick piston. This gives a capacity of 2cc each end at bdc.

In Tubal Caines book he gives the steam port in relation to the position of the crank. This will give a size relative to the stroke but does not allow for the size of the bore. Obviously a 20mm bore will require twice the air or steam as a 10mm bore with the same stroke.

Julian

 

[Blogwitch]

Julian,

Tubal Cain is right.

I don't think you need to worry too much about the cross sectional area of the port, even a very tiny one will fill a cylinder with time to spare.

The way I work mine out is to get the max swing centre points, then divide that distance by two. That will give you the maximum diameter of the port without getting any cross leakage at centre point. I usually just go down slightly on the size just to be on the safe side.

I have done a C-o-C to try to explain, I hope it helps.


John

 

[serhat]

Hi Julian,

Attached drawing may also help for defining the correct size.

Brgds