Steam w/ Vacuum Return

BAB

A couple of threads ago I discribed my heating system & some problems I was having. Some of you astute pros correctly jumped on the vacuum pump. I dismissed your comments & have been messing with the system ever since. All the time (3-5 weeks) my ability to pull a vacuum has been going down, down, down. I have finally accepted the hard news, ... the old pump has had it. I have pulled the the pump apart twice before to replace the shaft & gaskets. I know the pump impeller has had it, ... pitting, cavatation, erosion, chunks out of the impeller body, you name it. I can no longer pull a vacuum at all. It is currently acting as a condensaate return pump only activated by level control. Been in touch with the Nash guy & will have a new pump retrofit in 3-4 weeks.

My immediate problem is how to run the existing system for the next month or so. I can turn the pump off, close 2 valves & run my two pipe system with no pump or continue as is. Do I have to add air blow off valves on my steam or condensate return cause I am finding a lot of air trapped in the wrong places at the wrong times. What do I add to my 2 pipe vacuum return system to make it ok as just a 2 pipe system. Also do I continue with the pump or no pump. I have run the system before with no pump but have to run boiler up to 2-2.5 psi to achieve heating cycles. When I run with pump can achieve cycles with boiler outputting at 6-12 oz/sq in. Bromley

Ken_40

Are you absolutely, positively

dead-nuts certain, the pump only is blown?

A "hidden" leak would result in the same way as the blown pump.

On a temporary basis, you should be able to find a replacement impellor, just to "certify" there are no system leaks? ****, you resealed the pump, all the bolts are loose from inspection. Even if it's not an exact match, it may simply verify what you already know; but - it may also reveal something else!

Just being extra cautious. If I had a dime for every time I said pump, only to find the underside of some pipe laying on a previously un-noticed wet stain on dirt or concrete...

Bernie Riddle_2

Clarification

Maybe I misexplained myself. The pump is together & running now. The last time we pulled the pump apart the impeller was really defective, ... shot! We were shocked that it pumped at all, much less pull a vacuum. That pump tear down was 3-5 years ago.

I have learned this much about this site, ...your comments are going to be respected, ... I will not place the order for the new pump today. But finding an impeller for this Nash unit is not easy. I think that I am the only Nash vacuum pump owner in a 100-150 mile radius. Supposedly one of the few owners left in all New England. When you call pump shops for an impeller they look cross-eyed at you over the phone. If anyone can come up with an impeller, or a Nash Jennings 22 unit, or a trashed unit, ... I would certainly like to hear about it. See attached Bromley

BAB

Maybe I did not explain correctly. The vacuum pump is in place & running. (see attached) We did the last pump maintanence teardown about 3-5 years ago. The impeller at that time was so beat up that we did not think it could pump again, much less pull a vacuum. We were shocked, it ran & did pull a vacuum, ... for years. Just pulled less & less vacuum as time went on.

I have learned one thing about this site. The suggestions I get are usually on the mark. I will respect your advice. I told the Nash guy we will wait a bit on ordering a pump replacement. You understand that finding an impeller for a Nash Jennings 22 is kind of impossible. When I phone around to pump dealers & ask about a Nash pump they think I am crazy. I am one of 5 or 10 people that still have their Nash vac pump running in all of New England. If anyone knows where I can get an impeller, or a old Nash unit or a trashed unit, ... let me know. Bromley

Ken_40

I'm lovin' the home made separation chamber!

Nice touch. Probably works like a charm.

The reason I'm pushing on the impellor, or any part for that matter, is that pump "laws" were known by the dead men years ago. These laws suggest a common design of parts because all pumps behave the same given certain fundamental values and dimensions. These dimensions relate to the basic ones you might already assume; the shaft diameter the impellor is mounted on, the nature of attachment thereto (keyed, pressed, nutted, pinned, etc.) All of which can be interchanged easily with a little ingenuity - provided the shaft diameter and replacement impellor bores are equal, the next dimension, the outer diameter, is frequently "matched" on a lathe. When we bought a three piece pump from B&G they would have a guy chuck up the impellor (typically bronze) and reeduce the diameter on a simple lathe to meet our GPM or Head dynamic. So as long as a replacement impellor has enough "meat" to be close to what the original impellor's O.D. was, the motor will have adequate HP to make the performance required to equal what once was.

Next would be width. The replacement impellor must fit within the volute it is housed, and must fit snugly enough to not freewheel, but lose enough so it doesn't crash or bind in running position. The diameter of the eye of the impellor is to be considered too, but generally has a standardized ratio of the other dimensions to be somewhat unselectable, just whatever it is, it is.

The reason I'm saying all this is that Nash, like many other pump makers, did not have a bronze foundry or case casting facility, electric motor making factory, steel shaft machine shop, and seal making plant. They bought the components from various vendors or made a few components if large enough, to order. The hope being, that your impellor was identical to an Armstrong model zippidy-doo-da which also happens to be identical to the TACO model whackity-doo-da, as well as the Gould model hunkity doo-da...
But you need the critical dimensions to match 'em up, because a cross reference list was never created for volutes.

I'm sure someone somewhere could take your Nash vacuum pump's data plate and provide the two aspects of basic data that is key; those being: Feet of Head, and GPM flow rate. That, along with motor HP and RPM would allow two related but somewhat different ways to find a replacement impellor - perhaps.

The photos provided are good. A few close ups of the motor, cardle, shaft and mounting plate, might be even more helpful. The true nature of the pumps nature would be helpful. There were various "methods" used to create vacuum. Placing the impellor in a venturi shaped cavity was one. A so-called hurling tank pump-thru was yet another. Of course you don't have it, but twin-screw displacement pumps are also used. These look like a super-charger but are mounted externally.

A Dunham-Bush part may fit, National, out of Paterson, NJ had a presence through a few guys who tried to keep the line viable by rebuilding stuff similar to what you have.

In short, there may very well be an acceptable close enough impellor replacement out there you can cobble up, we just need to get the physical aspects down of the impellor itself, and the motor that drives it.