I am designing a 1.5 " x 1/5" two cylinder engine. Is there a formula or rule of thumb for determining the
clearance between the end caps and the piston face.
I will be incorporating cylinder drains on each cylinder.
Head spacing or clearance
Re: Head spacing or clearance
Any space is a waste of steam that has to be filled and emptied each stroke. Therefore the closer the better. However, stack up of part dimensions and expansion/contraction for a cold to hot engine needs to be considered. I use .050" for engines the size you describe.
Dave
Dave
Re: Head spacing or clearance
If you do not have any space at all, you cannot have low degrees of cylinder filling because of the outlet closing early which leads to too much compression work then. That is also a waste of steam.
Online program for valve gear design:
ValveGear Constructor [EN]
With automatic pre-optimization, DXF export, etc.
ValveGear Constructor [EN]
With automatic pre-optimization, DXF export, etc.
Re: Head spacing or clearance
When calculating proper head space in the past I have always been surprised how little clearance is really needed.
-Frank K.
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- Joined: Wed Jun 27, 2012 5:24 pm
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Re: Head spacing or clearance
Also need to account for changes in piston position over time due to wear. The piston will have to travel more to take up slack in the wrist pin and big end bearings.
On my shay, the new clearance is 1/16in at dead centers.
On my shay, the new clearance is 1/16in at dead centers.
-Tristan
Projects
-2.5" scale Class A 20 Ton Shay
Steam Siphon: https://www.shapeways.com/shops/leavitt ... tive-works
Projects
-2.5" scale Class A 20 Ton Shay
Steam Siphon: https://www.shapeways.com/shops/leavitt ... tive-works
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- Posts: 582
- Joined: Tue Jul 31, 2012 1:59 pm
- Location: Germany, Duesseldorf
Re: Head spacing or clearance
Agree!
Changing of dimensions cold/warm, wear/backlash of main rod and -axle and movement up/down of the main drivers demand for sufficient space
Otherwise volume of "dead" space will used during expansion and help for smoother running due to reduced compression.
Steam consumption of our small modell steam engines will be increased by almost nothing yet due to the much more important losses of both condensation and steam leakage
The worth of narrow clearance is overrated! Thus I used about 2 x 2 mm ( min. 1/16 ") - crosshead side slightly more than front - on my engines.
Just my two cents.
Best regards
Asteamhead
Changing of dimensions cold/warm, wear/backlash of main rod and -axle and movement up/down of the main drivers demand for sufficient space
Otherwise volume of "dead" space will used during expansion and help for smoother running due to reduced compression.
Steam consumption of our small modell steam engines will be increased by almost nothing yet due to the much more important losses of both condensation and steam leakage
The worth of narrow clearance is overrated! Thus I used about 2 x 2 mm ( min. 1/16 ") - crosshead side slightly more than front - on my engines.
Just my two cents.
Best regards
Asteamhead