Setting up a beam engine

[Astro]

Hi, I'm new to the forum and hope you can help.

A good friend of mine has built me a 'single cylinder beam steam engine with poppet valve' from a set of Julius de Waal drawings that are on the Model Engineering website for my 60th Birthday.

This was his first attempt at building such a model (although he is also building a steam locomotive for himself). The problem is that we are having problems in synchronizing the timing of the valve to the piston. I believe that this comes down to the relative position of the fly wheel crank (controlling the piston) to the eccentric (controlling the valve).

Any help would be greatly appreciated. Thanks, John

 

[Philjoe5]

John,
The usual practice is to remove the steam chest cover so you can observe the operation of the valve. The valve operating rod should have an adjustment for its length. Rotate the flywheel and observe that the valve covers or uncovers each port equally. If not, adjust the length of the valve rod so that this happens. Once this adjustment is made, then position the eccentric such that at top-dead-center, the port is just beginning to uncover and admit air or steam. Now rotate the flywheel to bottom-dead-center and confirm that the other port is just being uncovered. That should get you close.

If your engine does not let your have access to the eccentric when assembled then take this approach. Set the eccentric so that its maximum limit of travel in one direction occurs about 90 degrees from the location of the crank pin. This puts the minimum movement of the valve at either TDC or BDC. Then adjustments to the length of the valve rod are made for optimum engine running.

I've set timing in both types of engines. It usually involves a bit of fiddling until it works just right.

Cheers,
Phil

 

[Mechanicboy]

Use low airpresure to find the position of valve in the steam chest in both way where the airpressure is entered into the cylinder and mark up the position when the valve is opened to cylinder in both ways and set the valve in mid position in between the two marks and the excenter set to 90 degree from crankpin. Ready to run.

 

[RichD]

I've never built any steam engines, but in my 42 years of Refinery operations I've run probably dozens of different types.

The equipment I'm familiar with usually had the basic timing preordained by the bellcrank lengths and design. The slide rods were provided with adjustment nuts to allow the engine to be fine tuned for stroke length. Basically the nuts were on either side of each bellcrank and a gap (what I'll call deadband) was adjusted by turning the nuts.

I've adjusted the slide rods on steam driven reciprocating pumps while the pump was in operation. In general you control the stroke length by limiting the "open" time. you narrow down (shorten) the rod "deadband" travel to a minimum to shorten the piston stroke and of course the opposite way to lengthen the stroke. If you set the slide valves with too much "deadband" you'll hear a knock develop.

Don't know if any of that makes sense but that's what I always did. None of this may pertain to model engines since you're trying to run it for the very first time.

Rich

 

[vederstein]

Getting the timing right is one thing. The other is that the D-valve needs to be adjusted correctly. If it's too high to too low it will not cover and expose the proper ports properly.

Also, is the D-valve lapped to its sliding surface to keep valve leakage to a minimum?

...Ved.

 

[Astro]

Thanks for all your help. I'll give it a try.

 

[kvom]

OP stated it's a poppet valve, not a D-valve. The plans are posted here: http://modelengineeringwebsite.com/Beam_engine.html

The valve consists of two spools on a shaft that cover and uncover the steam passages. I imagine that when the beam is horizontal (mid stroke) the valve spools would be centered relative to these openings. Given that the same covers are used for both the cylinder and steam chest, it could be a challenge to adjust without disassembling. What may work is applying low air pressure and, with the beam horizontal seeing if air is escaping the exhaust ports. It appears that there is a some sort of screw adjustment on the valve rod that may be used to move the valve up and down. At mid stroke either both ports will be slightly open or both closed.

 

[RichD]

On my previous reply I was referring to equipment that had no flywheels or crankshafts to control the stroke. I probably shouldn't have replied to this post. My bad!
I get irritated when people post irrelevant stuff...then I do it myself.
Rich

 

[crueby]

OP stated it's a poppet valve, not a D-valve. The plans are posted here: http://modelengineeringwebsite.com/Beam_engine.html

The valve consists of two spools on a shaft that cover and uncover the steam passages. I imagine that when the beam is horizontal (mid stroke) the valve spools would be centered relative to these openings. Given that the same covers are used for both the cylinder and steam chest, it could be a challenge to adjust without disassembling. What may work is applying low air pressure and, with the beam horizontal seeing if air is escaping the exhaust ports. It appears that there is a some sort of screw adjustment on the valve rod that may be used to move the valve up and down. At mid stroke either both ports will be slightly open or both closed.

I've always called that a spool valve. Is the correct term poppet valve? I thought poppet valves were the mushroom-shaped valves like in a car engine? Which is correct? Or is this another case of same term/different meanings for different type engines?

 

[Swifty]

Spool valve is the correct term, a poppet valve is what they use in quick connect air fittings, that's just one example.

Paul.

 

[Mechanicboy]

There is not correct named in the plan of beam engine in post #7 : "poppet valve".. correct named is "piston valve" or as you can name it "spool valve".

 

[kvom]

The designer of the engine is from New Zealand, so I'm willing to give him the benefit of the doubt on the terminology.

In any case the valve is outside admission with both sides of the steam chest hole pressurized. The valve itself is 21 mm between the ends of the spools as are the edges of the inlet ports. When the valve is centered both ports are blocked, so no air should escape the exhaust outlet. The cylinder should also be in the center of its stroke.

When the valve moves down it opens the passage to the upper side of the cylinder to pressure and opens the lower passage to the space between the spools and thus to the exhaust. The piston will also descend, although the stroke of the piston and the valve will be different.