So what with the spindle in my pump?

[johnpenn74]

Can someone out there please elaborate on some pump design theory? I have a pair of 1" water pumps (looks like Wabco 11") and I don't understand the purpose of the horizontal 2ndary spindle for steam admission to the main cylinder. Why is the horizontal 2ndary spindle needed to admit steam? Is the d slide valve (removed from the pump in the pic) not adequit I see the 2nd spindle applied to several pumps but don't understand why it is required.

JP

[Mike Walsh]

You show two different views.

However from my understanding of the Little engines pumps, the horizontal spindle is likely a shuttle valve that changes direction of the passages thus reversing stroke.

Mike

[Brian Tusin]

John,

The valve in front that is connected to the trip rod controls steam admission to the shuttle valve in the back of the pump. Then the shuttle valve controls the steam admission that goes to each side of the piston.

Brian

[NP317]

The two-valve set up acts as an "amplifier", letting the smaller "trip-rod" valve control larger steam inputs to the cylinders via the shuttle valve.
~RN

[Erie2936]

John,
The valve in the back is what controls the steam admission to the steam piston. It is essential to allow the pump to reverse direction when the piston reaches the end of its stroke. This is a classic design employed for over 150 years by Westinghouse, Elesco, Worthington, National, etc pump manufacturers where they had a single cylinder piston driving a water or air compressor piston.

Consider a hypothetical pump design where the front valve, driven by the steam piston, also controls the covering and uncovering of each steam port to the steam cylinder. One port admits steam to drive the piston upward, the other port drives the piston downward. Lets also say that the valve is large enough in diameter to cover both valves at the same time. As the pump would start to cycle, the piston will move toward the opposite end of the cylinder. Just before the piston reaches the end of its stroke, the piston tugs on the trip rod and front valve such that you would reach a point in the stroke where both steam ports would be covered. Once that happens, the piston stops moving and the pump will sit there forever.

Now, lets say that we take this same pump design and make the front valve so that it just barely covers both steam ports, with the idea that at the moment one port is covered, the other port starts to open. This case will also result in a pump that cannot cycle, since there is no momentum in the steam and water pump piston while under load to allow the port to fully open and reverse the cycle.

I hope this helps.

[gwrdriver]

The two-valve set up acts as an "amplifier"~RN

Nice analogy.

[BillF]

The two-valve set up acts as an "amplifier"~RN

Nice analogy.

There is also a requirement for at least some time delay, which the two-stage valves provide. If everything in the pump responded instantaneously, all the moving parts would just settle down at one position. As it is, the second stage valve is always trying to "catch up" with the motion of the first stage, and this is what keeps the pump oscillating. Of course, there has to be gain, too. (Each valve triggers a larger flow of energy than the energy required to move the valve itself.)
- Bill Frensley