How long will the water last?

[sandy_ACS]

 

Hi PD's,

one of our new members aked how long 360 ml of water would last @ 40psi running his Home Built twin oscillating engine, which has a bore of 11mm and a stroke of 18mm.

Well here is how to work it out in fairly simple terms: -


To calculate engine steam requirements: -

1.  Multiply cross sectional area of bore x stroke to find swept volume of cylinder.

2. Since this is the volume of steam required to drive the piston from one end of the cylinder to the other, then for a double acting engine the same amount of steam will required to get the piston back to the starting point, therefore you must multiply this by 2 to arrive at the steam required for one complete revolution.

3. As you also have 2 cylinders, then you again must multiply the resulting figure by 2 to arrive at the total volume of steam for one revolution of the engine.

4. To find the amount of steam required per minute, at a given RPM, multiply the figure from (3 above) by the RPM.

So for a 2 cylinder, double acting engine having an 11mm(1.1cm) bore and an18mm (1.8cm) stroke: -

1.  Area = Pi x cylinder OD^2 / 4 = 3.14 x 1.1^2 / 4 = 0.950 sq cm

 Swept volume = 0.950 x 1.8 = 1.71cc.

2. Multiply x 2 for double acting  = 1.71 x 2 = 3.42cc

3. Multiply x 2 for 2 cylinders = 3.42 x 2 = 6.84cc = steam required for 1 revolution.

4. For 600 rpm = 600 x 6.84 = 4104cc steam per minute.

How long will 0.36 ltr water last?

Well, the first thing to calculate is exactly how much steam this amount of water can produce.
Unfortunately, the amount (volume) of steam produced from a given volume of water is not a constant, but is determined by operating PRESSURE, and it is, therefore, necessary to consult standard ‘Steam Tables’ to determine what this is for a given pressure.

At 40psi 1cc of water (1ml) will produce 474cc of steam.

So 0.36ltr (360ml) will produce 360 x 474 = 170640cc steam.

If you require 4104cc per minute then 17064/4104 = 41.59 minutes.

This figure assumes no losses, which is highly unlikely, especially with an oscillating engine, so it is normal to allow for up to 25% loss.

41.59 – 25% = 31.19 minutes.


I hope this helps you a bit.

Keep happy.

Sandy.

[Blow]

Thank you Sandy

This is the simple maths I understand and is just what I need to Know, sorry about the placement of the question but I'm very new to Forums and find it daunting with all the different sections, I'm getting better and starting to under stand the layout a bit more, I tired searching but came up with not allot.

My reason for trying to establish the running time was to help me decide where or not to build a small feed pump to keep the boiler topped up. If the answer was less than half an hour and I would but as it is about that and this is for my first project I think I won't bother as there are several other things I would / will change for the next project.

I'm still on a very steep learning curve but I'm really enjoying the challenge.

Thank you once again

[sandy_ACS]

 

Hi PD's,

Blow...... Happy to have helped a bit, that is, after all, partly what we are here for.

No need to apologies for the misplacement.... most of us have been guilty of it in the past, especially when topics get a bit heated, or sidetracked.

There are a number of steam articles in the 'Downloads' section that you might find useful which have been written by several different members of the PD's community, including an excellent article by 'Malcolm Beak' relating to boiler feed, water pumps and methods he has developed over many years of experiments. 
There are also quite a number of plans etc to keep you busy for 10,000 years or so.

If you have any further questions, just ask away... someone will always come to your assistance and provide an answer or at least point you in the right direction.

Remember... the only silly question is the one you don't ask.

Keep at it, and good luck with the new boiler.

Best regards.

Sandy

[derekwarner_decoy]

Hi PD's.......blow...a number of years ago I was considering a LARGER gas tank...when an experinced member suggested a GAS regulator....   it kills two birds with one stone

1) minimises gas consumption...totally adjustable...boiler water pressure piloted
2) minimises waste steam over the relief valve & hence water consumption

I chose an ANTON V71 model for just over EURO 100...plenty of good reading in our Steam folder if you are interested