Brown Vari Vac System

Charlie from wmass

I have a 1250 EDR system I am looking to add the vacuum pump back onto. Getting a run around trying to get a vacuum pump for this, any ideas guys? The original pump was replaced with a condensate reciever by a heating contractor who "new more" than the original engineer with his fancy expensive stuff.

Steamhead

As I understand it

the only difference in a Vari-Vac vac pump is the way it's controlled. Dunham used to make their own pumps, not sure if MEPCO still does. But if all you need is a vac pump, a Hoffman, Skidmore or Shipco unit should work. 

nicholas bonham-carter

Vacuum, the old fashioned way

Couldn't a system just be piped so as to fall into vacuum naturally, and stay that way during successive firings, and therefore have no vacuum pump?

If you look at the Hoffman system, there are a series of check valves to allow the air out of the returns, but not back in. A nice big drop-header (5-6 inches) could be an accumulator for the vacuum as it develops.

The first cycle after a long period of no firing pushes all the air in the supplies, and radiators out into the returns. As the system goes into a vacuum, the air left behind in the dry returns is sucked out through the check valve into the over-size header. In the second cycle, that air is pushed out through a Hoffman 76 vacuum vent in the header.--NBC

The Steam Whisperer (Formerly Boilerpro)

Don't forget Nash Jennings

They still make their very efficient vacuum pump

Pumpguy

We can help

Depending on the details of the existing condensate pump unit, we can offer a separate vacuum pump kit that can be used with the existing condensate pump set.  We do this all the time.  Our kits are very simple and do not require the use of cold city water.  Send me a PM, or call 1-888 853 9963 for more details.

Pumpguy

Vari-vac controls

Adding a vacuum pump is the easy part.  Controlling it can be the bigger problem. 



The easiest way to control a vacuum pump is with a vacuum switch.  The usual settings are off @ 8" Hg. vacuum, and back on @ 3" Hg.  But this doesn't give you a vari-vac system. 



Variable Vacuum Sup-atmospheric steam heating systems are 2 pipe type that rely on an outdoor temperature sensor. 



During the mild weather, 35 degrees F for example, the return line vacuum would be around 22" Hg, the steam main pressure is throttled to around 12" Hg. vacuum, and the steam temperature around 170 degrees F. 



As the outdoor temperature drops, these operating points also change so that with an outdoor temperature of 10 degrees F, the return line vacuum would be around 10" Hg. vacuum, and the steam pressure would be just a few ounces @ 212 degrees F. 



Back in the day, Nash sold such a system and the numbers above came from their sales bulletin.  Unfortunately I almost never see them in operation today.  I assume this is due to lack of maintenance of the controls, the steam throttling valve(s) and the vacuum pumps themselves.  I am sure lack of knowledge on the part of the operating personnel has a lot to do with it too. 

SWEI

Vari-Vac controls

if you can define the operating parameters (you have what looks like a good start in the post above) it should be relatively simple task for a DDC integrator (or a reasonably competent PLC hobbyist.)



If the pumps have 3ø motors, a VFD can be added to facilitate maintaining stable vacuum numbers.

Pumpguy

Vacuum pump VFD

The liquid ring positive displacement vacuum pumps frequently used for this application do not lend themselves to VFD and operate on a start-stop basis.  This is because the spinning ring of water (liquid ring) is the displacement medium (think piston) and is only stable through a narrow speed range for a given casing and rotor size.  Speed changes while operating can cause the liquid ring to become unstable.  

SWEI

No VFD

good info -- thanks.

Charlie from wmass

thanks for the info

I am not getting far with the one Steamhead listed, first one wants a system plan from an engineer, second says no pumps this small, third has not returned my calls or emails. Yet I am moving forward still. I am making contact with pumpguy to see what he has to offer. I will check out Nash Jennings. As for natural vacuum, the system is designed with no venting as the pump does that for it. So that would mean backed up air for the start of the cycles with out cutting in lots of new venting.

The originall control panel and valve for controling vacuum are in place, I just do not know if they can be rebuilt to work yet.

jumper

in the good old days

Water pressure was high,water in winter was cold, and best of all water was cheap. A water motivated ejector was inexpensive and foolproof. Now that water is expensive, a compressed air powered ejector is still foolproof. Suppliers are Fox,Penberthy,S&K, and others.