Piston rings

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Builder01
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Location: Erie, PA

Re: Piston rings

Post by Builder01 » Sat Jul 25, 2020 1:05 pm

Here's the link: (this should have been posted to begin with)
http://animatedsoftware.com/pumpglos/duplexpu.htm
This slide valve and cylinder have much more going on than in the "traditional" type of steam engine. The drawing I posted is nothing like the one in the animation, even though it was identified as being the same. It clearly is not. I hope the original poster can sort things out.

RET
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Location: Toronto, Canada

Re: Piston rings

Post by RET » Sat Jul 25, 2020 1:11 pm

Hi,

As you can see from my thread on the 1/8th scale cross compound air pump, I am finding out how those pumps work and I generally know how the duplex pumps work, but I haven't played with one yet. Perhaps some of the others can also help.

In the meantime, I'll tell you how I add pictures to my posts. Click on "Reply" the way you always do. Next, click on "Attachments." An additional section will appear below the "Attachments" area. In it click on "Add Files." in that area you can select any picture file (jpeg) you have on your computer and then double click it to add it to the file list. Cell Phone or camera pictures are what most people use. For example, the iPhone8 takes very good pictures as I'm sure do lots of other cell phones.

Note: The picture file you add must be 1.2 meg. in size or less for you to be able to include it in your post so you need a picture manipulation program like Photopaint or Photoshop to modify the picture file size, crop it etc. IrfanView will allow you to make the necessary changes as well. It will take a while for you to find out what works and how to use the programs.

When you want to add the picture, position the cursor in the text where you want the picture to be and the picture will be inserted at that point when you click on "add file." I find that it is best if you have a blank line above and below the picture addition point in the text.

Also, to see how the finished text and pictures will appear, click on "Submit" to see the finished result. If you aren't happy with the finished article, click on the pen at the top and that will allow you to go back and make any necessary changes. You can do this multiple times if you need to. I believe the pen will stay there until someone else adds something. It may also be time dependent.

This may be enough to get you started. Best of luck.

Richard Trounce.

Chickens
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Re: Piston rings

Post by Chickens » Sat Jul 25, 2020 2:06 pm

Builder - the drawing you posted is exactly like the animation. The drawing is not a very clear picture of the actual pump. It does not show the exhaust port hole. You need the other 10 pages of the print in a readable form.

Chickens
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Re: Piston rings

Post by Chickens » Sat Jul 25, 2020 2:41 pm

JPEG_20200725_153718_resize_87.jpg

Chickens
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Re: Piston rings

Post by Chickens » Sat Jul 25, 2020 2:50 pm

As can be seen the exhaust holes are drilled in 1/4" and 5/16" in from endcaps. They intersect with the steam inlet ports. As the piston is at it's maximum travel this port in covered up. As the piston starts its powerstroke the exhaust port is uncovered. (However) the valve prevents steam to escape through this port during the power stroke. ( see animation). This setup is to allow steam to enter the opposite end just before the piston maxes it's travel in the other direction providing a cushion.

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Builder01
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Re: Piston rings

Post by Builder01 » Sat Jul 25, 2020 6:29 pm

Now you have a third version which is clearly different from the animation and different from the drawing I posted.

In the animation, the slide valve is over 5 ports and the cylinder has 4 ports.

In the drawing I posted, the slide valve is over 3 ports and the cylinder has 2 ports. This is the least complicated and is most traditional.

In the second drawing the slide valve is over 3 ports and the cylinder has 4 ports.

No doubt you will sort this out, I am not sure that at this point it really matters though. Since you are using a published design, making the parts as close to the drawing will be your best bet.

Chickens
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Re: Piston rings

Post by Chickens » Sat Jul 25, 2020 7:35 pm

Builder the drawing you posted is from the blueprints I have. The drawing I just posted is from the same blueprints. The animation you posted is an accurate depiction of how this works. The pump is completed and has been working. Just not on steam. I have ordered some Viton rings and will make a new piston with two rings in each piston the way it was designed. Original design was with 2 bronze rings on each piston. That's what I did and they were working. They just failed for some reason. I need to find a ring/0ring that works hence the name of this thread. I did learn how to post a picture and a few things about 0 rings for piston rings. If you spend a little time and study the drawings and the animation maybe you will have a better understanding of how this works.

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Bill Shields
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Re: Piston rings

Post by Bill Shields » Thu Jul 30, 2020 6:04 pm

I would not recommend using 2 O-RINGS on a piston

if one o-ring does not work you are mis-applying it

piston rings are a totally different story...
Too many things going on to bother listing them.

Chickens
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Re: Piston rings

Post by Chickens » Fri Jul 31, 2020 10:50 am

Desigs calls for 2 0 rings. That's the only way it will work. I have made 2 new pistons with 2 viton 0 rings and have run it on air. It seems to run fine. Havn't tried it on steam yet but I think it will work. As stated before this is a different animal. Thanks to everyone for the advice. The information on piston rings is what I was after. It's been a big help.

Chickens
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Re: Piston rings

Post by Chickens » Fri Jul 31, 2020 6:05 pm

Screenshot_20200731-190017_Photos.jpg
Try to submit photo

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Bill Shields
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Re: Piston rings

Post by Bill Shields » Sat Aug 01, 2020 11:48 am

so...can you explain exactly WHY it will not run with just one o-ring?

Just because someone designed it with two o-rings, does not mean that it is a correct design.

Parker (major manufacturer of o-rings), clearly states throughout their manual that double o-rings is a bad idea

https://www.parker.com/Literature/O-Rin ... 205700.pdf

page 5-3, second paragraph down on the left:

A second O-ring may be used for the wiper, but it must not actually seal
because a pressure trap condition is likely to develop
between two reciprocating O-ring seals

From experience, the pressure trap between the rings can cause incorrect sealing since to correctly seal, an o-ring used in dynamic service must have a pressure differential across the contact surface. If a pressure trap occurs, then there is the possibility of equal pressure on both sides of the o-ring and it will leak.
Too many things going on to bother listing them.

Chickens
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Re: Piston rings

Post by Chickens » Sat Aug 01, 2020 1:46 pm

It has already been explained. I'll try again. There (has) to be a steam cushion at the end of the piston stroke. There is no mechanical mechanism (ie flywheel/connecting rod) that prevents the piston from slamming into the cylinder heads. That being the case the steam inlets cannot serve as the exhaust ports. As the power stroke commences the exhaust port in exposed, However steam pressure cannot exit this exhaust port because the slide valve is still covering it. As power stroke commences the steam exits the exhaust port on the other end until the piston covers it up and steam enters just ahead of the end of the piston travel. Pump will not function without two rings. (I've tried that) It will not work. Doesn't matter what Parker says. There are two different animations on utube. If you can slow them down you can see what's going on. Although one animation appears to be a bit out of time. That is the best explaination I can give.

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