Using a steam indicator

This forum is dedicated to the Live Steam Hobbyist Community.

Moderators: Harold_V, WJH, cbrew

k4kfh
Posts: 23
Joined: Sat Oct 06, 2018 10:08 pm

Using a steam indicator

Post by k4kfh » Sat Oct 20, 2018 1:03 pm

I'm a newbie to live steam, but I've got a little PMR #3 engine (horizontal, 1/2" bore, 3/4" stroke) and I'm working on a small boiler. I'm an electrical engineering student right now, but the old mechanical engineering tools have always fascinated me, such as the steam indicator. I am considering spending about $25 and building a "digital" steam indicator using an digital pressure sensor and a rotary encoder to measure the position of the crankshaft (so I can measure where the piston is in its stroke).

However, having never used one of these indicators or seen one in person before, I've got a couple dumb questions.

1. Would the pressure sensor just be connected to a pipe between the steam control valve and the steam chest? Or does the indicator actually have to be connected to a port directly in the cylinder (similar to a cylinder cock port)? I'm trying to avoid having to drill additional holes in the cylinder, as I do not have a mill.

2. Would you have a different indicator card for each side of the piston on a double-acting engine, since the piston rod reduces the effective area of the piston on the crankshaft side? Or is it usually such a small reduction in area that it's a negligible difference and you just use the same card?

3. Are there any differences in the indicators used on stationary Corliss engines and simpler stationary engines with piston or slide valves?

Advice appreciated.

RET
Posts: 756
Joined: Wed Jun 07, 2006 8:36 am
Location: Toronto, Canada

Re: Using a steam indicator

Post by RET » Sat Oct 20, 2018 2:50 pm

Hi,

Using a superficial Google search, it seems a steam indicator recorded the cylinder pressure vs stroke for at least one complete revolution of the crankshaft. Multiple revolutions should simply repeat the line drawn, provided that the load on the engine, throttle position and boiler pressure are unchanged.

For what you want to do, it would be important to have as little extra "dead volume" added to the cylinder as possible where the pressure sensor is attached since this will affect your measurements. Since on the indicator, the piston travel is represented as a straight line, the output from the crankshaft rotary sensor needs to be "straightened out" electronically so that it represents piston travel and not crank shaft rotation. I'm sure it is quite "doable," it is just another factor that needs to be considered.

If you do a search and my memory is right, you should find that the appropriate cycle for a steam engine is called the Rankine cycle. It is not as efficient as the Carnot cycle which has the maximum theoretical efficiency possible for a heat engine. Just as a matter of interest, the Brayton cycle describes a gas turbine engine.

In a model, for most practical purposes I think that the cross sectional area of the piston rod represents a relatively small reduction in area and could be disregarded. Besides, the indicator diagram measures pressure vs displacement, so piston area is not a factor.

Most of us are not really interested in the thermodynamic efficiencies of our engines; just getting them to run well is usually enough but don't let that discourage you.

Hope this helps.

Richard Trounce.

Steve Bratina
Posts: 946
Joined: Tue Jan 16, 2007 9:39 pm
Location: Cambridge Ontario

Re: Using a steam indicator

Post by Steve Bratina » Sat Oct 20, 2018 3:49 pm

I have used an indicator several times on both my stationary engines at home and away and I used to set one up on a friends traction engine when I took it to shows. As an instructor in college, I used to demonstrate its use to the kids mostly to help them sleep but some were interested.
The indicator takes a reading on one side of the piston only. The indicator card is affected by the whip in the actuating string that is used in the set up. The faster the engine, the less accurate the actual card if this "whip" is excessive. If using the cylinder drain as a feed point, make sure the piston does not cover over the outlet at this just wrecks the reading you are trying to get. If you are using superheated steam, an outside spring type indicator is what you require.
You can use a pressure sensor and a linear motion sensor to give you an electronic reading on a screen but that aspect never interested me so I can't give any more details then that. I used to have several different varieties on indicators, including a high speed indicator used for rotary airplane engines but I got rid of them all after my teaching days.
An indicator can be used for steam engines, gas engines, piston type air and refrigeration compressors, and even artillery guns. There are specific types though for the job required. You wouldn't want any brass parts in an indicator used on an ammonia compressor. The type of valve used on the engine has no bearing on the making of a card.
The tools needed to calculate the card could be a simple as a piece of paper and a knife but if you go on the great computer, you will be able to learn all about its use and calculating the card. Again, this is all the old school stuff. The electronic version you want to make is good too. Vacuum tubes may be hard to find though. That's is about all I have to offer here.

k4kfh
Posts: 23
Joined: Sat Oct 06, 2018 10:08 pm

Re: Using a steam indicator

Post by k4kfh » Sat Oct 20, 2018 4:54 pm

Steve Bratina wrote:
Sat Oct 20, 2018 3:49 pm
I have used an indicator several times on both my stationary engines at home and away and I used to set one up on a friends traction engine when I took it to shows. As an instructor in college, I used to demonstrate its use to the kids mostly to help them sleep but some were interested.
The indicator takes a reading on one side of the piston only. The indicator card is affected by the whip in the actuating string that is used in the set up. The faster the engine, the less accurate the actual card if this "whip" is excessive. If using the cylinder drain as a feed point, make sure the piston does not cover over the outlet at this just wrecks the reading you are trying to get. If you are using superheated steam, an outside spring type indicator is what you require.
You can use a pressure sensor and a linear motion sensor to give you an electronic reading on a screen but that aspect never interested me so I can't give any more details then that. I used to have several different varieties on indicators, including a high speed indicator used for rotary airplane engines but I got rid of them all after my teaching days.
An indicator can be used for steam engines, gas engines, piston type air and refrigeration compressors, and even artillery guns. There are specific types though for the job required. You wouldn't want any brass parts in an indicator used on an ammonia compressor. The type of valve used on the engine has no bearing on the making of a card.
The tools needed to calculate the card could be a simple as a piece of paper and a knife but if you go on the great computer, you will be able to learn all about its use and calculating the card. Again, this is all the old school stuff. The electronic version you want to make is good too. Vacuum tubes may be hard to find though. That's is about all I have to offer here.
So I would have to drill holes for cylinder drains in order to use an indicator on this engine? Or could I still get an indicator reading by just putting a tee in the steam inlet just before the steam chest?

The reason I ask is because it's a very small cylinder and as far as I'm aware, nobody even makes drain cocks that small. The smallest I could find were 3/16 OD and that's the size of the steam inlet pipe on this thing. I hesitate to try to drill holes in it since it's so small.

Thanks!

User avatar
Dick_Morris
Posts: 2155
Joined: Sat Jan 04, 2003 2:09 pm
Location: Anchorage, AK

Re: Using a steam indicator

Post by Dick_Morris » Sat Oct 20, 2018 5:07 pm

Go to archive.org and enter "steam indicator" as the search terms. There are a number of digital copies of old books available there.

To replicate the diagrams in the books you should use a linear sensor on the crosshead instead of a rotary sensor.

I agree that the volume between the piston and sensor should be kept at a minimum. But if the drain cocks are at the bottom of a horizontal cylinder, especially on a small engine, I suspect condensation will take care of a lot of the extra volume.

Getting diagrams from both sides of the piston allows you to compare the two to verify whether the valve events are equal. The unequal areas comes into play when you are calculating indicated horsepower.

I have an indicator that I got over 40 years ago because the price was right and I just had to have it, but I've never used it.

I got to watch indicator cards being taken on the Delta Queen HP engine many years ago. To step down the 10 foot travel of the crosshead, a plywood pulley, about 3 foot diameter, was mounted on a shaft and a cord was used drive it from the crosshead. A small pulley on the same shaft with a cord was used to drive the indicator, which had a spring loaded return. The DQ uses poppet valves actuated by levers and California cutoff. The cutoff was obtained by a spring driven release, independent of the valve actuating lever. Each time the admission valve snapped shut the indicator card showing a ringing due the a little bit of valve bounce.

From the indicator diagram you can calculate indicated horsepower. For that you need a planimeter, which is used to measure the area of an irregular shape such as odd shaped pieces of property from a survey, or an indicator diagram. The planimeter allows you to determine mean effective pressure (the P in the formula PLAN/33000").

User avatar
Dick_Morris
Posts: 2155
Joined: Sat Jan 04, 2003 2:09 pm
Location: Anchorage, AK

Re: Using a steam indicator

Post by Dick_Morris » Sat Oct 20, 2018 5:10 pm

The steam inlet is before the valve, the indicator must measure the pressure on the piston. If you aren't going to fit cylinder drains you can make the holes and use plugs. Or get a bigger engine. :)

Steve Bratina
Posts: 946
Joined: Tue Jan 16, 2007 9:39 pm
Location: Cambridge Ontario

Re: Using a steam indicator

Post by Steve Bratina » Sat Oct 20, 2018 6:37 pm

Some indicators required a drumbo pulley to reduce the stroke of the engine to 2" for the indicator drum. Some indicators came with a reducing mechanism which allowed reduction for several lengths of stroke. The Crosby indicator book can still be found in used bookstores with a good technical section. You can also find indicator instructions in certain ICS manuals.
If you get on the smokstak forum, there are some old heads there that know much more than me.
Remember, the indicator requires steam into and steam out of the one side of the cylinder to get a reading to calculate IHP (indicated horsepower)

Steve Bratina
Posts: 946
Joined: Tue Jan 16, 2007 9:39 pm
Location: Cambridge Ontario

Re: Using a steam indicator

Post by Steve Bratina » Sun Oct 21, 2018 6:02 am

Dam fingers. I just noticed and it should say a Brumbo pulley. The other term I should have used is reducing wheel.

RET
Posts: 756
Joined: Wed Jun 07, 2006 8:36 am
Location: Toronto, Canada

Re: Using a steam indicator

Post by RET » Sun Oct 21, 2018 9:55 am

Hi,

To make your steam connection, the easiest way would be to drill a 1/16" hole through the cylinder cover and make your pressure sensor connection there. As a temporary measure, you could epoxy the sensor onto the cover to hold it in place. Try and get the smallest size sensor possible because of the "dead volume."

For the piston position, you can use a rotary encoder on the crankshaft, or you can use a linear position encoder on the crosshead. If you are going to use the rotary encoder (which may be easier to connect mechanically), you need to continuously solve the equation for the length of the crosshead position. You know the length of two sides of the triangle (connecting rod length and crank length) and one angle (crank position), so its just simple math (trigonometry) to solve for the third side. If you use a rotary encoder, you will need to have a hall effect (or other sensor) to give a "home" shaft position for the pulse count to restart for each shaft revolution.

To do what you want, you need to have a look at Arduino boards. They are relatively inexpensive and have an host of sensors, LCD displays, etc. Since the entire system is open source, everything from different manufacturers works together. There are many different contributors of snippets of source code that you can put together to do what you want, and/or you can write your own code in C or C+.

With the Arduino board, solving the triangle equation is simple. The code can run and solve it continuously and you can get the system to show the indicator diagram output on the LCD attached to the Arduino board. The Arduino boards have both digital (on and off) and analog (continuously variable) inputs and outputs and some of the sensors can be powered from the board.

Just a nice little project, and it should work just fine. Doing it electronically should work better than the traditional way because there is no mechanical inertia involved as there is in the old systems. Because of this, the readout should be accurate to significantly higher speeds than what is possible with a mechanical indicator.

This should give you something to think about.

Richard Trounce.

B&OBob
Posts: 336
Joined: Sun Jul 22, 2007 8:27 pm
Location: Blue Bell, PA

Re: Using a steam indicator

Post by B&OBob » Sun Oct 21, 2018 10:54 am

Here is an article published by the PLS Gazette that covers the topic of steam engine indicators:
http://www.palivesteamers.org/pubs/gazette/2013_3-4.pdf
The article mentions two British model engineers who made serious, well documented tests of miniature steam engines using electronics-based indicators and reported in Model Engineer.

One of the researchers cited above used one cylinder of a 3.5" gauge Juliet as the test subject, and the other (later) tests were conducted with a specially-constructed steam generator and engine of reasonable displacement that even had temperature sensors embedded in surffaces of the cylinder. I'm sorry to be discouraging, but In the case of your small engine, relatively large uncontrolled heat losses will completely mask whatever P/V measurements you are able to make. It's extremely doubtful that anything smaller than a Stuart Turner 10V/10H, 3/4-inch bore/stroke, would yield meaningful measurements.

B&OBob

User avatar
apm
Posts: 185
Joined: Sun Jan 05, 2003 12:21 am

Re: Using a steam indicator

Post by apm » Mon Oct 22, 2018 8:48 pm

k4kfh wrote:
Sat Oct 20, 2018 4:54 pm

So I would have to drill holes for cylinder drains in order to use an indicator on this engine? Or could I still get an indicator reading by just putting a tee in the steam inlet just before the steam chest?

The reason I ask is because it's a very small cylinder and as far as I'm aware, nobody even makes drain cocks that small. The smallest I could find were 3/16 OD and that's the size of the steam inlet pipe on this thing. I hesitate to try to drill holes in it since it's so small.

Thanks!
Please don't take this to be an insult but your question shows that you are not fully understanding what a steam indicator card is trying to do. Steam pressure at the inlet just before the steam chest is supposed to be more or less at a constant pressure barring you opening and or closing the throttle. Steam pressure inside of the cylinder is a whole different story and what your indicator card is trying to measure. There is a whole book out there that describes the art of reading one of them so I will keep this short, but one of the key things that takes place inside of a steam engine is the expansion of the steam, and your efficiency is based off of this.

I don't know what you have for a steam engine but if you have something with a proper valve gear (with a reversing gear), you should be able to see what happens as you adjust cutoff. Cutoff is the amount of time the valve is open during the stroke of the engine. The shorter the duration you have the valve admitting the steam in the cylinder the more expansion takes place and the more efficiently you use your steam. The goal for maximum efficiency is to have the pressure at the end of your stroke as close to zero as possible. Any pressure remaining at the end of your stroke is wasted and exhausted unless you have a multiple expansion engine. As a result if you have pressure at the end of the stroke you are leaving energy on the table. Of course if you need to get more power say for example your locomotive is starting a heavy load you would adjust your cutoff so you use more steam but have more pressure through out the stroke. You will read stories and hear of firemen who complained about engineers leaving the bar in the wrong spot and making them work far harder to keep up pressure.

Steam engine indicators were something that peaked my interest at a young age when I had the privilege of meeting the great live steamer Howard Crouch. Sadly Harold has passed on but I remember as a young kid hearing him proudly shout out to me stories of how he lost his hearing sitting in a little basket on the side of the big Niagaras pounding down the rails at 75mph! I thought that was pretty darn cool. Fortunately his stories are quite well preserved at the following location for all to enjoy. https://nycshs.files.wordpress.com/2014 ... agaras.pdf Scroll down to page #17 and look at the picture of the guy sitting up in a temporary shelter pulling and indicator card right above the cylinders! That must have been a hell of a ride! Harold sure thought so and his stories sure captured the imagination of me as a young kid maybe 13-14yrs old. Maybe more on this site could chime in on Harold he was pretty much a steaming legend if ever there was one!

Outside of that yes it would make a lot of sense to try to do this electronically if one were to do it today that would be the only way it would be done professionally. Look at the link to the photos I posted about the amount of effort that went into taking indicators on the big Niagras. I think I see 8-10 people doing the work that could today be done with the help of maybe 5-10K worth of a DAQ system. Hell just the OSHA fines for blowing out a guy's hearing would cover the cost of the DAQ system in today's day and age. If a company would do that today they would probably deploy on several systems on multiple locomotives, stick a cellular link on the DAQ unit and unlike the engineers of Harold's era the data could show up real-time on the engineer's computer for advanced analysis. Or more likely if steam locomotives still rode the rails today every locomotive would have such a system as part of an on-board diagnostics suite the data would funnel thru a web portal where it would automatically be analyzed by computer algorithms, trends would be run against other similar engines in class, with emails sent to the train and shop crews showing them how they could improve their performance on the next runs all without a human touching any of it. If it sounds far flung it really isn't this is done every day on modern aircraft I know as I have seen it first hand in that industry. I have to think that GE's most advanced diesels are doing similar too. Modern technology is pretty neat isn't it?

So anyhow best of luck on your project it sounds like a lot of fun. Something I have always been tempted to do myself but never had the need.

Steve Bratina
Posts: 946
Joined: Tue Jan 16, 2007 9:39 pm
Location: Cambridge Ontario

Re: Using a steam indicator

Post by Steve Bratina » Tue Oct 23, 2018 8:30 am

What Harold and the many like him accomplished in his working life is nothing short of AMAZING. What computers do today is nothing short of amazing and we don't even need human intervention. We have come a long way.
As for exhaust, you can't have steam pressure at 0 because you need to close the valve before the end of the stroke to trap the steam and use it to cushion the stopping of the piston at the end of the stroke and help stop all the momentum of the attached parts to prevent excessive wear on the main rod bearing. Remaining steam is also required for exhaust on locomotives. It is also required for lubrication of the piston valve on the exhaust side to some degree.

Post Reply