Nash Jennings Vacuum pump

Double D

I can go back for more pictures but basically all but 2 of the discharge sides of the end of main F&Ts are below the dry return. When this vacuum pump is operating, does it have the ability to pull the condensate into the dry return? This is a small church with 4000sqft of installed radiation. The boiler is leaking now and will be replaced over the summer months.

Steamhead

@Pumpguy ?

Double D

Thank you @Steamhead just the guy I was looking for. He's helped tremendously in the past on these vacuum systems.

Steamhead

He's as good as it gets. Hopefully he'll chime in.

Pumpguy

I'm here, but don't know how to reply.

The vacuum pump's job is not to pull condensate back to the receiving tank, unless maybe you need vacuum to lift condensate from return lines that are below the inlet of the receiving tank. The condensate flows back to the tank by gravity, like rain down a downspout.

How's the pump working? Are you able to maintain a vacuum on the return lines?

Can you post some pictures of the pump package and nearby piping?

Based on the motor being a JM frame, the pump now fitted is a conversion and not the original Nash design. Original Nash designs used a 56J frame motors. I have a feeling this unit is now converted for pumping condensate only, and if that's the case, its just a condensate pump now, and can't pump any air to produce a vacuum.

What's the temperature of the returning condensate?

And what's the pressure cycle range on the boiler?

Attached is a cross section drawing of the original horizontal pump and motor assembly.

Really need more information to be helpful.

Double D

I only have 2 short visits to the church. The pump is running but I have not checked to see if it's maintaining a vacuum on the return lines.

I have a couple of pictures I can post of the package and nearby piping. I can get more if needed.

Returning condensate temperature at the pump is 200°. There are 3 failed drip traps close to the pump. Outside of the failed traps return condensate is 136°.

The boiler runs off a heat timer cycling at 4PSI.

Pumpguy

Thanks for the update. I was wrong about the motor frame size. It is a 56J frame. I got the JM from the motor's catalog number and rushed to judgement.

That said, these motors need to be re-machined to Nash Spec 22R to fit these pumps properly. You can't set the internal clearances properly with a standard off - the - shelf 56J frame motor.

This is an original pump and motor assembly that appears to have been recently worked on. How well it was put together and the internal condition of the working parts is something else again.

Can you tell me something about the cylindrical steel tank? What's that all about?

The first thing you need to do is get that condensate temperature down. The laws of physics just won't allow a pump to produce a vacuum at 200*F. water temperature. The attached file goes into detail.

The selector lever on the vacuum switch appears to be in CONTINUOUS. In this position, the lever blocks the control circuit contacts closed so the pump just runs continuous and does not respond to the float or vacuum switch.

I recommend for now your moving this lever to the FLOAT ONLY position. This blocks the vacuum switch's contacts open, so the pump will only run start - stop, controlled by the float switch.

Once the traps have been repaired and the condensate is down around 130 - 140*F range, you can put this lever in the middle FLOAT & VACUUM position. This will allow the pump to start and stop on demand of which ever switch is calling. The control circuit is in parallel, so when either the float or vacuum switch contacts close, the pump will run.

I recommend you change the boiler pressure control to shut off at 2 or even 1.5 PSI. This lowered pressure will still provide steam temperature at or above the 100% heat output rating of the radiation. This has the added benefit of there being less steam volume available to leak past a bad trap, so the returning condensate shouldn't be so hot. And most importantly, the fuel bill will be lower.

Now, about this pump's air removal volume capacity; 13 CFM. This capacity is just marginal at best, and it now being over 60 years old, probably somewhat less than its original 13 CFM capacity.

If I were specifying a vacuum pump for a system that required a 30 GPM condensate pump, I would want to see a vacuum pump in the range of 22 to 34 CFM of air removal capacity.

A separate floor mounted stand alone vacuum pump in these ranges could be added to this unit. Due to sales territory issues and pricing not allowed on this website, I can't go into greater detail.

If you'd like to discuss this further, please contact me directly and I will do all I can to help.

Double D

The motor was installed by their trusted electrician.

The cylindrical steel tank is/was used for adding chemicals.

You are correct about the selector switch. The pump runs continuous.

Top of my list was suggesting lower operating pressure.

Thank you for your help so far. This is a small church with a congregation of 80. I don't know how far they want to go with system corrections but with your help, they will at least know where they stand.

Pumpguy

Operating with the lowest possible steam pressure, and lowest possible condensate temperature are prime requirements for maintaining a reliable return line vacuum and lowest possible fuel costs.

If you could introduce some cold water to the valved off receiving tank, and then place the vacuum switch in the continuous mode, you will see what is the maximum vacuum the pump can achieve on a closed off tank.

With 70*F. water and the pump parts and valves in good condition and properly assembled, you could easily achieve 20" Hg. vacuum. You may have to pull up on the vacuum relief valve's stem so it doesn't bleed in any air at this high vacuum.

Whatever vacuum you get on a closed off tank is the maximum vacuum that can be achieved on an air tight system.

If the closed off maximum vacuum is considerably lower, the pump's not doing what it should.

If you want to really measure the pump's air pumping capacity, you can perform an orifice test. The attached file goes into detail. Don't be afraid, its not as complicated as it looks.

For your pump, a 7/32" orifice bleeding air in from atmosphere should show 8 - 10" Hg. vacuum on the gauge.

As always, feel free to contact me directly with any questions.

Pumpguy

In looking at your first set of pictures, it appears that the outlets from all of the F & T traps are below the return lines. This doesn't comply with proper practice which calls for a down hill gravity drain out of the traps.

In order for these traps to drain, there needs to be a pressure differential between the steam side and return side. One of the traps looks like there's more than one foot of uphill piping before it connects to the return line.

I'm not the best guy to comment on these piping arrangements. A working vacuum pump would certainly create the needed pressure differential, but there may need to be some piping changes to the outlets of these traps too. Maybe a lift fitting arrangement would be needed at each trap's outlet. If yes, a return line vacuum on this system becomes even more important. Hopefully others will comment.

Double D

The outlets of the F&Ts were one of my major concerns. I did do some searching to see if maybe a lower pipe that maybe ran along the wall could have possibly been removed when the updated F&T traps went in. Haven't found any trace as of yet. Only 3-F&T traps in the entire building drain properly. 

Pumpguy

I seem to recall someone recommending installing check valves at the outlets of F & T traps piped like this, but being a pump oriented guy, I didn't think about it too hard.

Usually when there's just one trap piped this way, I suggest a mechanical lift as shown in the attached file. With the number of low traps in this system, I don't think that's practical.

EBEBRATT-Ed

Maybe run the low F & Ts to a small condensate pump that could lift the water to the return or pump it back to the boiler. F & Ts can lift water if you have enough steam pressure but not the ideal way to do it.

Double D

I would love to get the condensate to a small condensate pump. I see plugged tee's with grouped returns in the basement. Possibly there was one there and someone took it out thinking it was OK to do? I find it hard to believe this system always operated with all but 2 F&Ts below the dry return. It's definitely something to consider. Thanks. 

Steamhead

We ran into a similar situation with traps piped so the condensate had to go up. Here's the link showing our solution:

https://forum.heatinghelp.com/discussion/169680/found-a-new-vapor-species-triumph

If possible, I'd do the same on this one. No need to introduce more mechanical complexity, and a transfer pump's shaft seal can leak vacuum.

Double D

Interesting. Part of the problem is the numerous doorways. I'm guessing this basement was finished off long after the church went up in 1911. There may have been piping like that originally but it may have been in the way so someone decided to remove it. 

Steamhead

As long as the traps stay in place, running the pipes under the doorways should work. The water will flow through them by gravity.

Pumpguy

If the return lines are piped under doorways, and then back up to a higher return line, you'll need a way to deal with air too. For this, you'll need an overhead air line. This is a classic Door Loop piping arrangement.

If using a condensate pump as a mechanical lift, you'll want to vent the receiving tank to a vacuum line, and not just to atmosphere. If just vented to atmosphere, you will loose any vacuum on the return lines that drain into the condensate pump's receiver tank.

See attached files on the above 2 comments.

Also, its important that the condensate pump's receiver tank be suitable for vacuum service. Some condensate pump receiver tanks are made from light gauge sheet metal that can "oil can" flex with pressure changes, and their float switch linkages are not air tight.

109A_5

Hello @Double D,
As @The Steam Whisperer noticed and mentioned in the other thread, some of the original vacuum lift fittings seem to be now missing. I'm wondering if it is simpler (and less cost) to just restore the system rather than to re-engineer it. I'm thinking most or all the traps should be as shown below with the vacuum lift fittings.

Pumpguy

Actually, a constructed lift fitting doesn't have to be as complicated as shown in the drawing. A common plumbers P trap will work just as well, only the flow is uphill instead of downhill.

The idea is to use vacuum drain the upstream horizontal pipe to the bottom of its run, which a common elbow won't do.

Also, the upflow pipe is reduced in size for the purpose of increasing the velocity through this pipe.

Another comment about the vacuum pump itself, there are no #164 spacer shims between the motor end bell and the pump's port plate. This means there is more internal clearance between the port cone and the rotor's taper bore. This is the most important setting in the pump and with this clearance not properly set, the pump's air volume capacity (CFM) is sure to be lower than it could be.

Double D

When I spoke to the building trustee today he did admit there's a chance he removed lift fittings when he replaced the F&Ts over the years. I do plan to get over there to check the vacuum pumps performance as is. Also do a more detailed view of the system. All of the advice on this post has been extremely helpful.

Pump operation has been addressed over the years but never pump performance. 

109A_5

Hello @Double D
Is this trap mounted sideways ?

Double D

Hello @109A_5, Now that you mention it, it does look like it's sideways. One more thing to look into when I get back there.

Steamhead

I've seen traps that look like that. The inlet is above the two side outlets. IIRC Barnes & Jones and Sterling made traps like this.

In the pic, the trap on the left looks like an old Webster. That might be a clue as to the original system design.

109A_5

Maybe it is a B & J 41T

Double D

B&J 41T center inlet, right or left discharge. Maybe it's not sideways. 

jumper

>>If using a condensate pump as a mechanical lift, you'll want to vent the receiving tank to a vacuum line, and not just to atmosphere. If just vented to atmosphere, you will loose any vacuum on the return lines that drain into the condensate pump's receiver tank. <<

Doesn't venting to atmosphere –like most one pipe– necessarily let air into system?
I've seen setups with vented receivers along with degas machines. Confused me.

ttekushan_3

I have half a building full of just your arrangement of f&t traps below return. As @Steamhead said it’s probably a Webster system as I have stewardship over. Originally it was all gravity return with two building wings with underground return. Around 1959 dozens of water cooled air conditioners, cooling towers, make up air coils were added and importantly, underground returns were abandoned and run overhead on ground floor along side the steam mains. There were already two condensate pumps added in one wing (improperly piped for vac, since corrected); I’ve added two more but there are limits! (5+ buildings stitched together built at different times. It’s a maze- a fun one but a maze nonetheless). So half the building mains and all under basement window convectors have to lift condensate. The window convectors have 32” of lift. 

@Pumpguy is correct with 1.5 to 2.0 psi suggested supply pressure. With just a few inches of vac those pressures clear the traps completely in our application. 

Be aware if a condensate pump is chosen that proper piping be observed for vacuum i.e., the vent line attached to vacuum return as well. 

PS all the make up air coils had lift even if for no apparent reason. Every single one froze at some point. That part of the system’s been completely removed 

Double D

@Pumpguy, I was able to get over to test the vacuum pump. The best it would do is 2" vacuum. Are 164 spacer shims the next step or is there something else you could suggest. My guess is a new vacuum pump may not be an affordable option at this time. 

109A_5

Double D said:

The motor was installed by their trusted electrician.

Pumpguy said:

Another comment about the vacuum pump itself, there are no #164 spacer shims between the motor end bell and the pump's port plate.

Double D said:

Are 164 spacer shims the next step or is there something else you could suggest.

Looks to me (by the paint) the motor and pump assembly was changed as a whole assembly at some point and the tank may be original or much older.

If the #164 spacer shim is missing, but is actually needed for proper operation, whoever assembled the motor to the pump made the paint match very closely, but left out the #164 spacer shim and apparently did not test the assembly for proper operation.

I wonder maybe if it did work fine at one point (without the #164 spacer) and now the pump is just tired from running continuously. Is rebuilding versus replacement a less expensive option ?

Double D

@109A_5 Since they are into the expense of replacing a leaking boiler, they are hoping to get by with repairs/corrections to the vacuum pump. 

109A_5

Hello @Double D

To me, looking at the "SCI cross section" adding the #164 spacer shims may be more complicated than loosening the nuts on the studs that secure the motor, then adding the shims and securing the nuts. There may be a procedure to determine the correct shim thickness.
Also changing just the motor looks even more complicated, possibly more than an electrician would want to get into. To me it seems like the motor and pump assembly was changed (without the tank).
Kind of makes me wonder what actually happened.
Maybe it was sent out and the job was not done correctly.

Double D

Hello @109A_5,

More complicated was a thought.

Pumpguy

Its SOP to paint the pump & motor assembly after repairs are completed. I do that all the time.

If the motor wasn't re-machined to Nash Spec 22R, the pump's air rotor will bottom out against the taper of the stationary port cone before its hub comes in contact with the shaft shoulder. Shop cut internal shim washers can be added to space the rotor away from the cone so the assembly can rotate. I see that all the time too.

Time and performance testing will tell if pump is still suitable for this system's vacuum needs. If not, there are larger vacuum pumps that can be added to this receiving tank.

Double D

@Pumpguy How do I go about getting this pump re-machined to Nash spec 22R?

Also, I thought of maybe checking the existing vacuum breaker and swing check for leaks after I left. Could vacuum possibly be lost there?

Pumpguy

Pump has to produce vacuum (pump air) first before we need to be concerned with air leaks. You can remove vacuum relief valve temporarily and use pipe plug instead. With only one air check valve now, its open when pumping air so no concern. If you had a 2nd vacuum pump, air check valve becomes very important. With vacuum pump A running, air check valve on vacuum pump B needs to be air tight to prevent air short circuit.

Send motor, or pump parts too, to me, and I'll quote needed repairs including re-machine the motor and assemble the pump.

Otherwise I can provide the dimensions and how to set up the motor in a lathe for machining to Nash Spec 22R.

Other choices including a separate conversion condensate pump to fit existing receiver tank and larger separate vacuum pump.

Edit: See my earlier post on performance testing. Lets get some test results first, then decide what to do next.

jumper

How much air and down to what vacuum is typical? How is the water for pump cooled?

Pumpguy

For sizing a vacuum pump's air removal capacity, there is no hard and fast rule to use. Everything depends on the air tightness of the system and the temperature of the returning condensate.

Back in the day, 1/3 of a CFM per thousand Square Feet EDR was adequate, and is a rule many manufacturers of this equipment still use today.

Recognizing that today in almost all cases a new vacuum pump is going on an existing system, the conditions are something less than new, a larger air removal capacity (more CFM) is needed. So, that said, I like to go with one (1) CFM per thousand square feet EDR. This can be tweaked depending on the intended system's conditions and the CFM of available vacuum pumps. One thing is certain, it is difficult to err in providing too much air removal capacity.

The typical and most common return line vacuum operating range, the vacuum switch settings, are to run until 8" Hg. vacuum is reached, and when the vacuum bleeds back down to 3" Hg. the switch contacts close until 8" Hg. is reached again.

To get cool condensate, the traps must be in good condition and not leaking steam, the return lines
preferably not insulated, and the supply steam pressure be as low as possible. The problem comes when we have institutional or industrial installations where the steam is also used for other applications like cafeteria steam tables, sterilizers, or manufacturing processes.

For applications like these, I like to recommend a separate condensate pump to handle the hot condensate, and the cooler condensate from building heating radiation go to the vacuum pumps.

Condensate can also be cooled by running it through a shell and tube heat exchanger upstream of the vacuum pump, using the hot condensate to pre-heat cold water for DHW. Obviously, a large and constant volume of DHW would be needed for this scheme to be successful.

jumper

Are these pumps different from the liquid ring pumps I used to see in industrial applications like drying?

Pumpguy

jumper said:

Are these pumps different from the liquid ring pumps I used to see in industrial applications like drying?

Sort of.

In addition to the liquid ring rotor for pumping air, they also have a centrifugal impeller for pumping water.

Earlier designs have both the rotor and impeller spinning together by the same motor inside a common housing. Later designs have separate single purpose pump and motor assemblies; a separate pump and motor assembly for pumping air, and another separate pump and motor assembly for pumping condensate.

jumper

For those industrial applications I remember that cooling the water for the ring was important. Vapor pressure limited how low a vacuum could be achieved. Some applications even used some sort of oil instead of water. Vacuum pump salespeople tried to introduce more efficient equipment but liquid ring was valued for its ruggedness.

If the OP cannot repair the Jennings he can consider other methods to generate vacuum. An air powered venturi eats electricity but is fool proof.