Air Pump D Valves

[FLtenwheeler]

Hi All

I am working on 2 air pumps. The supplier specifies Stainless Steel for the D valves. I am under the understanding that Stainless Steel is a poor bearing material. The cylinder is Silicon Bronze. I was thinking of using Aluminum Bronze for the the valve because I have it.

Thanks

Tim

[Bill Shields]

that will work....good luck machining it

[steamingdon]

I have used 303 ss. on valves against brass with 100% success . it is a steam chest, so I think this would work on bronze as well.

[FLSTEAM]

I agree with Bill, good luck machining it.

JB

[Harold_V]

I agree with Bill, good luck machining it.

Take note that the material mentioned (by steamingdon) was 303 stainless, which is free machining. 416 would be a nice choice, too. Much nicer to machine than low carbon steel. While these alloys don't make a great bearing, so long as they are not run against a like material, they most likely will serve perfectly well. 304, 316, 321, 347? Yeah, they can be trying.

H

[FLSTEAM]

I was referring to Aluminum Bronze. Hard to machine....

JB

[daves1459]

I've run up against several aluminum bronze alloys over the years. They ranged from incredibly difficult to machine to moderate. I've had good luck on small to medium model parts with alloys with 13% or less aluminum using high speed steel tools as long as they are dead sharp. Micro grained carbide end mills with a high helix work well. Cast alloys have been easier to work with than wrought. Aluminum Bronze 954 is good and is available in continuous cast round bar. It has 11% aluminum, machines reasonably well, and wears excellent.

There is an article in the current issue of Live Steam about building a steam feed pump. The author claims his design does not require lubrication. His D type steam valve is made of PEEK HPV. I've researched this stuff and it has definite possibilities. I have a steam pump project coming up and am going to give it a try. It is available through McMaster-Carr. Search McMaster-Carr part #1595A11.

Dave

[Dick_Morris]

PEEK HPV

Yikes! 1 inch diameter by 1 foot $141.05. Good to 480 degree f.

[daves1459]

PEEK HPV

Yikes! 1 inch diameter by 1 foot $141.05. Good to 480 degree f.

Yeah, but for the little valves for a feed pump wouldn't a 5/8" diameter at $42.11 a foot or 3/4" diameter at $56.84 a foot do?

Dave

[James Powell]

Even if it is $150/ft, and you use what ? 3" let's say...well, I know that if I put in more than 4 hrs work into the part, that my pay is more than that...and that's as a power engineer, using work's equipment not mine...

So yes, a $40 piece of material is "annoying" in the expense account. But if it takes you 2 days to convert it into a part, that's about $2/hr worth of "fun"...

Sometimes we loose sight of what the costs are in this as a hobby, and focus on things that are expensive, even when they take a lot of time to complete. (Hi Dad...how did the 8 BA bolt making go ?). There does come a time and place where spending money makes more sense than spending time. Unless this is a 0 dollar hobby for someone, in which case it can be done, but you pay with time rather than money to do so. Not a one of us is getting younger- even me !

James

[Bill Shields]

Which is why 100's of these pumps have been successfully built and operated using 303 stainless valves

[daves1459]

Which is why 100's of these pumps have been successfully built and operated using 303 stainless valves

The first two pumps that I built had 303 stainless steel valves and they worked well. That is as long as lubrication was present in adequate amounts. Almost as soon as the lubricant was missing scoring started. I guess it can be said "Well, make sure lubrication is always present.". Yes of course, but I believe it is safe to say live steamers often have trouble getting reliable consistent oil delivery from usual inline hydrostatic lubricator. I have rebuilt other pumps and valve seat scoring was always part of the repair. Besides, with lubrication there is always the brown gooish residue that collects around the piston rods and runs down the pump body.

From my point of view an oil-less feed or air pump is a desirable goal. I'm of the opinion that with modern materials all that is left for a lubrication free pump is the D slide valve. The PEEK material offers a chance to solve the lubrication problem and can be used with lubrication if so desired thus reducing the sensitivity to scoring. The PEEK material suggested available from McMaster-Carr is carbon fiber filled to retain shape under pressure that is a problem with plastics and is impregnated with PTFE for lubricity. As I said I have a pump project coming up and plan to give it a try. Hopefully it will work well. If it doesn't there is always 303 stainless and a lubricator.

Anyone who has had a slide valve throttle in their steam dome knows that metal on metal combinations are difficult. Some have gotten away with Teflon for the slide. If this PEEK stuff works out it will be a candidate for throttle applications. I'm not ready to risk that yet. I'm going to try it in a pump first.

Dave