Valve port size question

[Peter H]

I have a Hasbrouck 1 engine. It is built around a cylinder sleeve. The Hasbrouck #10 engine is basically the same engine but uses a cast iron block instead of a cylinder sleeve. The thing that I notice is that on my engine the intake ports and exhaust port are all the same size. On the number #10 engine the exhaust port is 50% larger than the intake ports. My question is-when I try to run with the Stephenson linkage partially closed the engine runs very lumpy, not smooth at all. Could this be from my exhaust port being too small? Is my engine being choked? Modifying to the #10 design is doable.
Thanks-Peter

[fredrosse]

The exhaust passages should provide larger flow area than the high pressure steam passages, as the larger volume of exhaust steam results in higher velocities, and high pressure drop.

Having stated this fact, there are many steam engines that function satisfactorily without increased exhaust flow area. I do not think this condition results in "lumpy" operation. With linked up valve gear, the torque pulses inherently become more "lumpy". This becomes more noticeable with a smaller engine flywheel. A valve linkage with improper design or adjustment, especially too early steam admission before the piston reaches TDC/BDC exasperates the problem.

To check for engine steam inlet"lumpy" kickback with early steam admission, put a few PSI air pressure onto the engine, and turn it over by hand. This will et you get an idea of where the "lumpy" behavior is occurring, and can generally be improved with adjustment of the valve mechanism. This usually results in reducing eccentris's angle of advance.

In summary, the "lumpy" engine issue is probably not due to the size of the exhaust passages. Especially with an engine of proven design, and Ray's engines fit that category.

[Peter H]

Thanks for the reply. Can you think of why Ray Hasbrouck made the change in port size when everything else is the same except for the change from cylinder sleeve to cast iron block? He must have seen some advantage.

[fredrosse]

Perhaps (actually almost certainly) Ray knew larger exhaust passages are better, so he incorporated this feature easily on the later design.

[dampfspieler]

Hello Peter,

Ray made the changes to the exhaust ports because he found in practice that engines with a larger port cross-section simply run better and secondly I think it is possible that he took a closer look at STUART Turner's designs and found that this is basically how it is done and the small engines where this is the case were operated at nominal speeds of 1000 rpm.

Incidentally, Ray chose the ports on all of his engines to be too narrow for a moderate steam supply speed. I have more than doubled the cross-section of the steam ports from the slide mirror to the cylinder ends on my HASBROUK #10 and in combination with the significantly larger flywheel the engine now runs silky smooth.

You can watch a video of the engine running in condenser mode here -

------------
Dietrich

[Peter H]

Thanks for the info. One of my winter projects will be to modify my engine to increase exhaust port size and steam passages .

[rolphill]

When I was writing my thesis on steam engines, my professor found a valve passage size equation in an old engineering book.

It's on a tab in my big steam engine spreadsheet that I posted elsewhere here, but here it is:

Recommended Minimum passage area (in^2) = Piston area (in^2) * Mean Piston Speed (ft/min) / Constant

Mean piston speed(ft/min) = RPM * (Stroke(in) / 6)

For the constant: 9000-15000 for inlet, 6000-7000 for exhaust. If same passage use exhaust.

This is for the passages between the valve and the cylinder though. For actual steam lines there are calculators online that will tell you the pressure loss across a given pipe diameter for a given steam pressure and flow rate. You just need to calculate your engine's expected mass flow rate.

[barts]

These are the same calculations I used when I designed Otter's original engine, a converted refrigeration compressor.

- Bart

[Peter H]

I did the calculations using the formula provided by Rolphill and the passages for the Hasbrouck #1 are ok, so modifying my engine is probably not worth it.