Set up of float and discharge on vlr

aircooled81 · June 2016

B&g vlrs condensate vaccum pump for cast iron steam boiler.
I'm going to be setting up the float on one soon, i'm concerend the lack of a throttling valve, and wrong float height may be flooding the boiler. I also have a condensate return issue on start-up I'm trying to sort-out, but if the float level is too high this may be my dilema.
I think if the sump is taking too long to eject the condensate, it's allowing the make-up water to fill. See the make-up water is filling off of an automatic feeder based on boiler level.
No, i'm not going to replace the feeder, let's not go down that path.
Anyone have some words of wisom on maintaining a hoffman/b&g condensate vaccum pump, and advise on set-up of the floats?
Would the addition of a throttling valve help meter the fill when the pump ejects?

Ohh ya, and I need to set the vacuum cut-out. I think it runs around 8 to 10" but I dont remember. I plan on lowering the boiler steam pressure, it's set to cut-out at 4psig currently. The darn pressuretrol is a range of 2 to 10psi, so I might not get it too low, as I have read at the bottom of the range pressuretrols dont operate as consistently.
Any opinions here?
I'm thinking about setting the pressuretrol to 2psi cut-out and adjust the cut-in to 1psi. Shortcycling may be a concern here, so I think I'm going to test it a few times before I commit.

Steamhead · June 2016

Hope @Pumpguy will chime in.................

Pumpguy · June 2016

I will....

First of all, unless it's a boiler feed unit with pump controlled by boiler level controls, please understand that the purpose of this pump is to MOVE condensate, NOT TO STORE condensate. The industry standard storage capacity for condensate pump tanks is one minute with boiler @ max steaming.

If you're having a problem with a starve - then - flood condition with condensate at the boiler, then I would think the problem lies with the boiler not having enough water storage capacity to fill the entire system with steam.

When this happens, the boiler runs out of water before the whole system is filled with steam. So, then the boiler takes on make-up water and continues to fill the system with steam.

Now, when all that steam condenses and comes back to the pump, it just pumps it back to the boiler, but the boiler being being too small to hold all that condensate it gets overfilled; flooded.

This is a common scenario when an old large volume boiler is replaced with a modern one. Same steaming capacity but less water holding capacity.

The only solution that I know of is to add a separate boiler feed storage tank, with feed pump(s) controlled by water level controls on the boiler.

This boiler feed storage tank should be sized based on steaming capacity of the boiler and desired amount of steaming time. A typical steaming time would be 10 minutes, although I feel better recommending a tank that holds 20 minutes worth of water.

Something else to consider is missing or non-functioning equalizer line and/or valve.

When steam stops flowing in an air tight system, the condensing steam creates a deep vacuum. Unless equalized with the pressure in the return line, this induced vacuum will hold condensate out in the system. This held up condensate could cause a low water condition at the boiler. When the pressure finally does equalize, this held-up condensate now overfills the boiler, causing a flooded condition.

As far as the vacuum pump goes, for most systems, the on - off range setting of the vacuum switch is off @ 8" Hg. and back on @ 3" Hg. providing an average 5.5" Hg. system vacuum.

You really shouldn't need more than 2 PSI steam pressure at the boiler, unless steam is used for other purposes besides building heat.

If you are interested in measuring the capacity of your vacuum pump, it is really quite simple to do. I won't go into detail here as this is explained in detail in our website

In addition to the mechanical condition and air pumping capacity of the vacuum pump, the air tightness of the system and temperature of the returning condensate play a big part in overall vacuum performance.

Feel free to contact me off line if you have specific questions.

jumper · June 2016

If the system is airtight why is there pressure in the return system? Doesn't pressure equalize whenever traps open?

aircooled81 · June 2016

Jumper can you elaborate on your question, not sure if you were asken me or Pumpguy

aircooled81 · June 2016

Pumpguy,
I can post to you offline if you prefer. But for anyone else who would be interested in the details....
First off, thank you for the detailed reply. I thought it to be very insightful.
Boiler is Pearless 211A 19.9hp, 2083 steam edr, 39.55gal water content.... How do I determine the rate at max steaming? I'm not familuar with that term, so I am very interested in this.
The condensate pump is 10VLRS1-20, basically 14GPM 20PSI 6CFM 5.5"HG. Is 14GPM the capacity or flowrate? Maybe I'll try some math and try to figure it out?
The pump is rated for 10,000sqft edr, so is grously oversized.
It's a special capacity model, but I don't know to what degree makes it special?
I have not timed this unit, and have only visited it once or twice. I'm going to perform the service the iom recomends and look into it's operation this week.
What I witnessed in the past was the boiler fire up, pump start-up, and water level in boiler drop to fill (auto float style fill) before the vacumm pump sent back any condensate. When the pump finally sent the condensate back, It didn't climb above the sight class completely but it certainly was 4/5 full if not more.
There is an operable equalizer line on the boiler, it actualy drops into a Hartford loop, and the condensate return I think (by memory) is directly into the Loop.
Regarding system vacuum, I have seen this boiler fire at about 2psig and cut out at about 4psig. I don't have any reason to suspect vacuum on the supply side at this moment, but thank you for that insight aswell. I don't remember but there may be a few zone valves though, and I will have to investigate this. That could certainly cause the vacuum you suggested.
All the radiators are pipe in, pipe out through trap. None of them have thermostats, but I suspect two or more zones do have thermostats and that may be where my zone valves are.

Would you agree my condenate/vacuum pump is grously oversized? Aside from leaving bricks inside (just kidding, old toilet tank trick) is there a viable solution for this instance?

Would the boiler feed pump storage tank you suggested just be between the discharge of the condensate pump and the inlet of the condensate return at the boiler?
If so, can it be up high and just gravity fed, so no extra pump is required? Or is this a large storage tank better suited on the ground? And do you recommend a particular model water control?

Pumpguy · June 2016

@Jumper, The equalizer on a 2 pipe system comes off the top of the steam header, then makes a horizontal run through an uncovered cooling leg through either a dropped swing check valve or 3/4" thermostatic trap, then drops down into the return line. This allows the induced vacuum from condensing steam in the header to equalize with the (positive or negative) pressure in the return line. Once the pressure is equalized, condensate can flow by gravity back to the pump's receiver.

@aircooled81, Yes, I agree this unit is oversized. A 20 HP boiler only needs a 3 GPM condensate pump, which will handle 2X this boiler's steam producing capacity.

One Boiler Horsepower will make 34.5 lbs/hr steam @ 212*F. One Boiler Horsepower will serve 140 Sq. Ft. EDR, so a 20 Hp boiler will serve 2800 Sq Ft. EDR. The basic rule of thumb for sizing condensate pumps is 1 GPM per thousand sq. ft. EDR.

What you really need determine is how much time your boiler will run continuous to boil off the water to where it will call for more, or shut down on low water.

If your boiler runs out of water before the system gets all the steam it needs, then you need a separate boiler feed storage tank with feed pump. This would be installed in series between the vacuum pump and boiler.

The condensate stored in the boiler feed tank would be fed to the boiler on demand of a low water controller on the boiler. The usual arrangement is for the controller to start and stop the boiler feed pump.

If your vacuum pump's tank is too big for your boiler, it's going to starve-then-flood the boiler. You can try to close up the float switch range and decrease the start-stop cycle time to keep condensate moving to the boiler. Depending on what float switch is installed in the vacuum pump's tank, you may be able to install a shorter radius float arm which will also decrease the start-stop cycle time.

I have often thought about some other way to feed a boiler from a boiler feed tank without using a pump, but haven't come across anything on the market to do this. Your idea may have merit, but I've never seen it done.

Just keep in mind my first post opening paragraph: The purpose of a condensate pump is to MOVE condensate, NOT TO STORE CONDENSATE. Storing condensate is a boiler feed tank's job.

Hope this is of some help.

jumper · June 2016

>>I have often thought about some other way to feed a boiler from a boiler feed tank without using a pump, but haven't come across anything on the market to do this. Your idea may have merit, but I've never seen it done.<<

Commercial places where there's budget and headroom can elevate tank.Especially when boiler feed is boiled for degassing.

Set up of float and discharge on vlr

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