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[pipercub1772]

hi allan hear new member, i have a twin cyl engine 3/8 bore 1/2 " stroke it has 2 springs holding the cylinders together side by side they are about 3/16 dia  5/8 long each with a 90degree turn at each end to clip around the posts on each cylinder unfortunately one is damaged i think they are stainless steel dint know if they are compression or tortion springs any advice would be wellcome also  were to obtain any from

[logoman]

The twin Graupner has springs like that, but I don't know if they'll fit, perhaps someone else will know.

[andrewh]

Hi, Allan,
welcome to the steaming world of Mayhem

I'm not an expert on Steam, so regard this as a holding reply till the experts dive in.

The springs you describe hold the cylinders onto the port faces on an oscillating twin - it seems that all twins use similar springs.  They may well be available as a spare.  I would ring Tony Green or one of the other steam spares suppliers (I will dig out URLs when I get a minute and post them)

John, (Bogstandard) has made series of this type of engine, so will certainly know where he got/made them from
 the type of spring is just a simple tension spring, and yes, they are probably made from stainless wire

The power of the spring is difficult to describe - it has to be just strong enough to hold the cylinder block onto the port face against spring pressure (with no leakage) but no more, or power is wasted in friction. 
As a polymer person I would (if you need a short-term fix) use either a length of silicone fuel-tube or a slice cut from a bicycle inner tube
as temporary springs  (both silicone and butyl rubber are perfectly happy at these temperatures and will last forever.  How you fix them will depend on the actual fittings at each end.  Probably there is a peg on the cylinders (to fit the loop on the end of the spring on) so cut a thin length of strip fronm either the fuel tube or inner tube (maybe 1/8 wide)
Punch a hole in each end so that it is stretched maybe 1/8th, and see how she works.  adjust the "spring" tension  by punching alternative holes to stretch it more or less.

If you are of the scientific bent, you could measure the existing spring - diameter, wire diameter, free length and stretched length and calculate the spring tension using  basic engineering principles and Hookes Law*. 
Or pin one end to a wall, hang a clamp on it (any reasonable weight that stretches the spring a small amount) then make a ruber spring the same basic length that stretches the same amount - Then Your'e close! 

Intended to be helpful
andrew

*"Ut tensio sic vis" is how he published it!

[bogstandard]

Allan,

As Andrew states, they are just a basic tension spring.

I have thousands in a box that I have gathered over the years, so I just grab what I need to do the job.

Don't worry about it being stainless, there is plenty of oil about on these engines, and you will find a normal plated one won't go rusty.

You can usually buy boxes of assorted springs on market stalls and cheap pound type shops.

I have attached a little sketch on how to do it. I would suggest you make a new matched pair, and retain the old one as a sample.

They are a little fiddly to do, I use a pair of electricians wire snips to do the cutting and bending.

You don't show your location in your profile, if in the UK I would have sent you a few samples for you to play with.

If you are from the UK, either PM or email me with your full name and address complete with the diameter of the spring and overall length (including loop) and you will have an early christmas present.

John

[andrewh]

Allan,

That's Mayhem for you
You wait minutes for an expert, then John replies

No mechanical or electromechanical thing gets thrown away in our house till my son and I have investigated it to bits.  Anything useful (motors, electronic components, springs, pulleys etc)  are thrown into boxes for re-use.   

andrew

[bogstandard]

Actually, Andrew has got his polymer bit almost right.

There is a continental maker that uses silicon o-rings for the springs, just stretched over the pegs. I don't know how long lasting they would be, but with the cost being so low, you could always have a few spares in your box.

I actually bought one special spring last year, from an engineering supplier, just a compression spring, but with a specific SWG for the wire. It was 1.5" long by 1/4" diameter and cost over £7 by the time they added a handling charge (picking it up out of a box).

So if you see any knocking about, pick them up and save them.

John

[andrewh]

Thanks, John
I spent 5 years designing industrial polymers and elastomers, I hoped a little had rubbed off!

Silicones (or polysiloxanes to their friends) are all happy up to 250 degC more or less permanently, and some are designed for up to 400degC (continuous).  Steam temperature in a model steamer is about 130DegC, so in the worst case the metal is less than this and silicone will be fine - hence the use as piston "o" rings

Similarly Butyl rubber - all inner tubes are butyl - is happy at 150 forever, but is not staggeringly elastic.  Enough to work, however

Please no-one read any more and suggest Viton  -good stuff, but please don't.  Leave it to the defence wallahs who can deal with free Hydrofluoric acid

I have specfied and purchased special springs (gas turbine overspeed bolts) and they were priced by the Kg - same price for one or about 300, cos the setup and testing was most of the cost
andrew

[derekwarner]

Hi all....we have a few misnomers  here....& I will not use the complicated technical names ..... ....as  we are talking about conventional O-rings

a) NBR = synthetic nitrile rubber & OK for 105 degrees C in an encased environment
b) H-NBR = an hydrogenated version of synethic nitrile rubber & OK for 150 degrees C in an encased environment
c) Viton...or FPM = is technically rated to 200 degrees C in an encased environment...& yes at elevated temperatures does produce HF....
d) Silicone = has a higher elasticity & lower friction coficient than Viton & also a higher tear resistance  than Viton

Our model steam engines @ 30 PSI generate approx 150 degrees C

So go to your bearing distributor & ask for two 16 x 2 section silicone o-rings .....& the result may be OK...as long as you purchase a bag of 200 pieces @ $1.????? each

However ...I am talking about the internal engine o-rings..........not the 'hold together bands' ...as offered by others .......................Derek

[bogstandard]

A member over on Paddleducks put up a link to a German made engine, and I thought it was very relevant to this article.

http://www.kassner-dampfantriebe.de/Produkte/Schiffsdampfmaschine_Nanus/schiffsdampfmaschine_nanus.html

This is a tiny steam plant, but notice the way the cylinders are held onto their faces.

Rubber bands anyone?


John

[andrewh]

Everything Derek says about "o" rings as seals working in compression I agree with - tho he has missed out

e) Ethylene Propylene Diene Monomer (EPDM) happy at 150 Deg C continuous and water and air, but will swell in oil

These are the "o" rings sold in B&Q for water duty - seals in taps etc.  These will live forever in air, and would also be suitable to hold steam engines together.

Nitrile and H-nitrile have no resistance to sunlight and ozone and will fail in days is stretched in the open air.  (hence the reference to "encased")

"o" rings work in compression, generally in a well lubricated environment (in a steam engine anyway). 
We are expecting these to work in tension in air at moderate temperatures
Misnomers? Que?
andrew

[derekwarner]

Hi.....Andrew...I intentionally left EPDM out of the equation as most WEB page provide two temperature ratings...as below

Ethylene propylene has a temperature range of -65· to +300· F (-54· to +149·C) for most applications.

EPDM IS RECOMMENDED FOR:

Phosphate ester base hydraulic fluids (Skydrol, Fyrquel, Pydraul) - Steam to 400·F (204·C)

See how they nominate +149 C for most applications then requalify to 204 C for steam

As we know saturated steam leaving our model boilers is in the order of 150 degrees C ....but even with a lagged line to the lubricator & then to the engine I suspect we have a heat loss of say 15 degrees C?????

In our Port Kembla steel industry  we have only one furnace application that uses a phosphate ester fluid i& hence EPDM for valving interface o-rings...with the  cylinders using using alternate seal element elastoner [vast majority of high temperature applications use either water glycol or Quintolubric 833-300]...so I have little experience with EPDM elastomers

I believe my French JMC3H engine has FPM piston seal elements & Teflon sheet gaskets between the cylinder headcaps & endcaps + the cylinder to valve body faces

regards Derek

[andrewh]

Just for general information - EPDM is the universal rubber used for water systems, water-based hydraulics, steam hoses and use in open air (and phosphate ester based hydraulic fluids) . 
It is less good around oils and greases  - it absorbs them and swells up which may, or may not, prevent it doing its job.
Everyone know it very well - even if they are not aware of the fact since all hoses in car cooling systems are EPDM and most of the rest of the door seals*, trim parts etc on a car are EPDM too.   All  domestic water pipe seals, tap washers and other rubber bits associated are EPDM too - so he packs of o rings you buy in DIY stores for replacements are EPDM. 
Useless for oil seals, but good for use as rubber bands in the open air!

*yes, these are normally made as Thermoplastic Rubbers (TPRs)  - most of them are mixtures of EPDM and polyethylene

I would certainly use if for steam pipes, probably piston seals, and it would be very suitable as a lightly stretched spring on a steam engine in fresh air.
andrew