Confused by basement runs in school 2 pipe system

Pumpguy · May 22

Still don't understand "connected to the vacuum assembly". Could you show pictures?

If you're meaning the vacuum (air removal) function is regulated or controlled by the aquastat, this generally isn't a good idea. Especially with that 2 step lift in the lower level.

Air removal and pressure reduction is often needed even though the returning condensate is cool, or hasn't started coming back yet.

Now if you converted this portion to a mechanical lift with its own condensate lift pump, that would be better, but still IMO, not a good idea.

EBEBRATT-Ed · May 23

In the picture that shows the radiation that sure looks like a vacuum lift fitting par way up the wall. Sure seems like a lot of lift is needed. You kind of have to blow up the pic to see it.

heattheschool · May 23

Yes, that’s what I mean. The aquastat is regulating the vacuum function (vacuum only turns on when steam is in the mains). It looked recent change (the electrical conduits are cleaner and shinier), that’s why I brought it up.

makes sense that it isn’t ideal. Yet another opportunity to improve things. :)

mattmia2 · May 23

someone kludged that in to stop the vacuum pump before the steam leaking past the traps gets to the pump?

heattheschool · May 23

yes. It goes up about 64” per section of the vacuum lift. More than a foot more than recommended by the references from @Pumpguy for a 2-stage lift.

heattheschool · May 23

https://forum.heatinghelp.com/discussion/comment/1856220#Comment_1856220

Can’t be that, see the picture I just put up. That’s the primary steam pipe it is attached to. I’m not really sure why someone did it.

mattmia2 · May 23

oh, so it is just turning it on when the boiler starts heating?

heattheschool · May 23

yeah. Not sure why it isn’t just turned on with the boiler power though so it would start to pump vacuum before the pipes got hot.

mattmia2 · May 23

maybe because it isn't allowed to go in much of a vacuum it is to wait until the boiler is steaming so it is pulling steam from the boiler instead of air in through the vacuum breaker

heattheschool · May 25

I found @Pumpguy has previously explained the equalizing line and atmospheric-vented boiler feed pump.

https://forum.heatinghelp.com/discussion/180306/steam-boiler-seems-to-be-pulling-a-vacuum-causing-it-to-shut-down-on-low-water

There is an equalizer line from the vacuum receiver/tank to the steam main, as shown in the previous diagrams. The vacuum pump outlet goes to the boiler feed tank though.

The feed tank is vented to atmosphere (looks like a standard Hoffman watchman condensate feed pump). The vacuum breaker on the boiler may be there to prevent flooding the boiler from this tank when it shuts downs.

It looks like the suggested solution is to put a valve in the feed line that is controlled by the same signal as the feed pump.

Am I understanding this correctly? What type of valve makes the most sense here?

heattheschool · May 25

I finally made a really rough diagram for what I think is happening. I am sure I'm missing some aspects and the diagram is really rough, I'll translate it to a better drawing program or P&ID software soon, but hopefully this helps you all understand what I think I'm seeing for the piping.

EBEBRATT-Ed · May 25

@heattheschool

I have a little booklet "Some Basic Principles of Steam heating Systems" put out by Nash Vacuum Pumps in 1955 mine is a 1992 reprint its like 23 pages and the print is tiny. But it is all about vacuum pumps and piping.

Perhaps @Pumpguy has this and can post it I think it would help you a lot.

I would send you mine but I can't give it up yet LOL

I am going to try and scan and post but the print is tiny and I am having trouble with my printer. Will see.

EBEBRATT-Ed · May 26

I don't understand from your diagram how your system can maintain a vacuum. The vac pump will pull a vac on the entire system (or try to) but when the boiler goes into a vacuum it will pull air through the open vent on the condensate tank….not good, I don't see how your system can achieve a vacuum.

I do not claim to be a vacuum system expert (like @Pumpguy ) but have worked on a few and don't think I have seen the set up you have.

Pumpguy · May 26

I have a few copies of these booklets left. The pages are composed of reduced copies of the pages Nash last published in their heating pump engineering data book in 1966. We printed a run of these booklets back in 1992 to help promote our Type CLS vacuum heating pumps which we introduced at that time.

We still offer these latest design Type CLS vacuum units.

The pages I post here from time to time are full size copies of these pages.

In this particular case, I don't believe the problem of the induced vacuum caused by condensing steam in the boiler resulting in the boiler being flooded by atmospheric pressure pushing feed water from the vented boiler feed tank is covered in these pages.

The solution to this problem is to remove the swing check valve on the discharge of the boiler feed pump(s) and substitute a motorized or other type of normally closed positive closing valve.

This positive closing discharge valve needs to be controlled by the boiler water level controls. When the boiler needs to take on feed water, the boiler feed pump is energized and the valve should open. When the boiler water level is satisfied, the boiler feed pump is de-energized and the motorized valve should close.

When the motorized boiler feed valve is closed, atmospheric pressure can't push feed water from the vented boiler feed tank into the boiler even if the boiler is at a vacuum, i.e. a pressure lower than atmospheric.

A simple swing check valve won't work since it only stops flow in one direction, away from the boiler. In this case we need to control flow in both directions, toward and away from the boiler.

mattmia2 · May 26

I assume you also need a throttling valve on the feed pump so the level doesn't change quickly between when the controls sense the need to open the valve or close the valve and when that actually happens.

something like a taco zone sentry or other motorized ball valve with the feed pump controlled off the end switch of the valve?

EBEBRATT-Ed · May 26

@mattmia2 Its normal to have a balancing cock on the feedwater pump discharge to:

Keep the motor from overloading. The feed pump will pump more water with the boiler at 0 pressure than it will at say 10psi so the balancing valve needs to be adjusted for that.

Also it should be adjusted to keep the pump on for a decent time and not shortcycle on and off with the pump control.

One of the most popular valve for feed water control are the Belimo valve (although you can uses any motorized valve) 120 volt is typically used.

The pump control on the boiler (usually a McDonnell Miller #150) makes contact on a boiler water level drop and opens the feed water valve. When the valve is partially open the end switch on the feed water valve closes to start the feed water pump.

The feed valve can either spring return to a closed position or be driven closed SPDT

EBEBRATT-Ed · May 26

@Pumpguy

I agree with the "reduced copies of the pages", almost need a magnifying glass LOL. Good information though.

Pumpguy · May 27

https://forum.heatinghelp.com/discussion/comment/1856553#Comment_1856553

I'd be happy to provide full size scans of any particular page you might need. Just specify the page number and your email address and I'll send off to you.

Confused by basement runs in school 2 pipe system

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