Timing position for walschaerts valve gear

[Michael CallaghanParticipant @michaelcallaghan68621]

Hi out there. After watching a few videos on utube, I have the following question. I do understand how to get the TDC position of the motion using marks on the cross slide, or main driving wheel. However am I correct in thinking that in TDC the piston should be almost at end of its travel towards the front of the cylinder with space to allow the input of steam to enter the cylinder. The bobbin to be just allowing steam to enter the piston cylinder to force the piston back.
or should both the piston and bobbin be in the centre of their cylinders. Sorry if this is dumb, but only a fool never asks a question. Thanks

[Michael CallaghanParticipant @michaelcallaghan68621]

[noel shelleyParticipant @noelshelley55608]

TDC is the piston at it's furthest point of travel in one direction the other end is BDC ( Top and Bottom ). I will leave others far more able to deal with the valve setting, but my understanding would be that at T or B DC the valve would be JUST starting to open. Good Luck Noel.

[duncan webster 1Participant @duncanwebster1]

What Noel said, plus the little bit open should be the same at TDC and BDC, and it shouldn't change as you alter cutoff

[Michael CallaghanParticipant @michaelcallaghan68621]

Thanks chaps, just one more thing. Let’s say the right hand piston is at TDC, in what position should the left hand piston be. Thanks 

Edited By Michael Callaghan on 18/01/2023 16:52:15

[duncan webster 1Participant @duncanwebster1]

Assuming 2 cylinders, just to the BDC side of centre. The Angularity of the conrod means its not bang on central.

[Paul KempParticipant @paulkemp46892]

Posted by duncan webster on 18/01/2023 17:47:40:

Assuming 2 cylinders, just to the BDC side of centre. The Angularity of the conrod means its not bang on central.

Are you not 90 degrees out or is the loco quartered at 180 degrees? With locos and TE’s it is more helpful to refer to front dead centre and back dead centre rather than top and bottom.

Paul.

[duncan webster 1Participant @duncanwebster1]

Calling extremes of travel centres is confusing, but established terminology. I should have said the other side will be just to the BDC side of halfway position, then it would be clearer.

[Michael CallaghanParticipant @michaelcallaghan68621]

Thanks chaps

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