Trevithicks Dredger Engine

[Paul HorthParticipant @paulhorth66944]

Here is a further update on running the Trevithick engine, four months on…

Following a holiday, and then a bout of unexpected faults and troubleshooting, I have recently had a series of successful runs. The engine will now run continuously for the duration of the gas, about 30 minutes, at a speed around 160 – 140 rpm. This is still faster than I would like, but at least it doesn't stop. On compressed air it will run quite a bit slower. The pump works well, the flame stays alight from just the steam draught. The steam is restricted by an orifice 0.029 diameter, in the throttle valve, but even so the speed is very sensitive to the exact position of the throttle. I start at 20 psig and this pressure then drops to around 12 – 15 psi, where it is held steady.

All the operating conditions of this boiler and engine are just about in balance with nothing to spare:

• The burner flame using a No. 5 jet is just about sustained by the engine draught through a 1/32 blast nozzle
• The burner burns just enough gas to make enough steam to sustain the pressure at the lowest regulated speed throughout the run. Faster speed causes the steam pressure to fall. The gas pressure falls as the tank empties, for 3 reasons – the gas is consumed, the tank gets colder, and the propane comes off first leaving gas richer in butane which has lower pressure. The gas control valve has to be gradually opened to compensate for this. The average gas flowrate is 0.45 to 0.5 gm/minute.
• The pump delivers just about enough feed water to match the steam rate (about 5 gm/minute) without needing a bypass. I did fit a bypass but I run with the valve closed.

I have not yet got the level gauge to function.. The level is visible before steam is raised but then it just bounces randomly. I will next make a deck to fit on the plinth so that all the feed piping is below the deck.

This thread doesn't really belong in the Beginner's Questions forum, but I don't know how to move it to a better place.

Paul

Edited By Paul Horth on 10/12/2017 19:11:53

[Paul HorthParticipant @paulhorth66944]

Error alert:

I was incorrect to say in the last post that the gas consumption will reduce the gas tank pressure. If the liquid in the tank is one component, (propane, or butane) and at a constant temperature, then the pressure will stay steady as the gas is used, until all the liquid has evaporated. For a mixture (LPG) the pressure will fall even at a constant temperature. I knew this professionally but was too hasty to check before sending my post. Apologies.

Paul

[Author]

Posts