Vacuum pump piping

bigpete638

Hello,
A maintenance working changed the pumps on this vacuum receiver and was pulled from the job. I was asked to reconnect the system but can’t find any literature on this particular unit. Any information is greatly appreciated.

bigpete638

I can see where the discharge of the pumps tie in and where it connects to the return to the boiler. There is a half union on the line next to it. Is there supposed to be a vent?

bigpete638

I’m not sure where the bottom line coming off the unit tied in.

bigpete638

I order Dan Houlahan’s book and just started reading it. I’m a steamfitter but have always been a new installer. Never piped a vacuum pump before.

ScottSecor

@bigpete638 It's not that simple to explain. Here is a starting point:
http://documentlibrary.xylemappliedwater.com/wp-content/blogs.dir/22/files/2012/07/DN0134E.pdf

From your photos it appears you have ITT/Domestic Pump/Hoffman unit, similar to the link I provided above. Yes, the tank has to be vented, typically well above the top of the boiler level. Yes the condensate has to be pumped back to the boiler, typically well below the boiler water line.

ScottSecor

The vertical pipe coming off the two check valves above the tank are likely the condensate return that would go to the boiler. The vertical pipe coming off the top of the tank would likely be the vent (to keep the tank from ever pressurizing. The other opening in the tank is for the return lines to tie in. The thing under the silver gauge is a basket strainer (that occasionally get clogged), I urge you to clean it and prime it before starting unit for the first time. Finally, those pump motors are far from original, be real careful with them as rotation is critical and they may not be the correct motor for your application.

Might consider reaching out to the local ITT/Hoffman/Bell & Gossett (now Xylem) representative for some help and perhaps repair parts.

bigpete638

Once again thank you. Several buildings here were already converted from vacuum return to gravity via condensate receiver tank. The piping was never changed either. Lots of problems but they’re ridiculous about cutting corners and saving money.

ScottSecor

One more thing to consider, based on the owner cutting corners and the age of the steam traps in your photos, I'd be very careful. As you may already know, vacuum pumps do not work well with even slight amounts of live steam. Unless all or at least most of the steam traps have been rebuilt or replaced, I'd suggest not running the vacuum side just yet.

bigpete638

I just found out they are no longer using it as a vacuum system and are just hurling water to the boiler.

jumper

bigpete638 said:

I just found out they are no longer using it as a vacuum system and are just hurling water to the boiler.

Properly designed vacuum systems are rare.

bigpete638

Trying to locate these traps online for replacement. F&t traps with an exterior thermostatic element? The supervisor did mention he wanted to restore the vacuum system as opposed to gravity.

Pumpguy

@bigpete638, you will find in Dan's books that it's never a good idea to remove a vacuum pump from a system that was originally designed for a vacuum return.

Unfortunately, this happens all too often, resulting in a need to operate with higher steam pressure, uneven steam distribution, longer warm up times in mild weather, and increased fuel costs.

Can you tell us what is the returning condensate temperature and operating steam pressure on this system? If over 2 or 3 PSI, its too high. Even the Empire State Building, which is a vacuum return system, doesn't go over these pressures.

To elaborate on @ScottSecor's comments, If the condensate temperature is much over 165*F, the performance of the vacuum pump will fall off. I would consider 170-175*F to be a maximum condensate temperature for a vacuum return system. Lower is always better for efficient vacuum operation.

High condensate temperature usually starts out when steam traps fail and allow live steam to enter the return lines. This can be exacerbated by an increase in steam pressure, which causes an increase in the mass or volume of steam that leaks past the bad trap(s).

Depending on the particular condensate pumps now installed, it is possible to continue to use these in conjunction with a separate stand alone vacuum pump. You don't always need to install a whole new vacuum condensate return pump set. Feel free to contact me directly for more details on how this can be done.

bigpete638

I just started this position two months ago. They actually have been dumping condensate down the drain I believe. Couldn’t tell you the temperature but I’m sure you already have a good idea what it was.

bigpete638

There are accessible traps to replace but the surrounding piping is old. If a thread snaps(which happens regularly here) I’m dealing with asbestos(which we can’t touch because they don’t have funds to abate).

jumper

bigpete638 said:

I just started this position two months ago. They actually have been dumping condensate down the drain I believe. Couldn’t tell you the temperature but I’m sure you already have a good idea what it was.

I've seen quite a few industrial facilities dump condensate. Factory sewer has drains all over. But it looks like in your case they have piping to return condensate to boiler room?

bigpete638

They do have return piping but they disconnected the tank and ran the line directly back to a tempering tank. I’ll be tying back into the boiler here soon.

EBEBRATT-Ed

@bigpete638
Those are Dunham-Bush traps but I don't think they are made any longer.

You could try Tunstall associates in Chicopee, MA or Barnes & Jones in Boston for parts to repair those traps.

Other than that replacement is a nasty Repipe. I had a building in Connecticut with 600 of those traps. Nothing fits even close. best option we found Tunstall has some in line F & T traps that you can pipe in fairly easily but you have to watch the capacity. The inlines have lower capacity as I recall

You can put other traps in of course with more repiping

bigpete638

Can I use f&t traps in a vacuum system?

bigpete638

I’m planning on replacing the whole manifold along with all the traps. I just need to find out which traps would be best suited for this application. The Dunham bush traps look just like f&t s with an external Thermo dynamic element. Was wondering if a f&t trap would also function in a similar matter?

ScottSecor

I am not certain but bit I believe the existing traps in your photos are F&T traps, just that the "T" (thermostatic) is external instead of the more typical internal type. Yes, a normal F&T trap will work fine.

bigpete638

I’m am indebted to this site. Thank you for all your help.

Steamhead

Dunham-Bush is still around, now called MEPCO. AFAIK they still make trap parts. If not, what @EBEBRATT-Ed said.

And listen to what @Pumpguy and @DanHolohan say. Pumpguy is the best when it comes to vacuum. When you see them say "it's never a good idea to remove a vacuum pump from a system that was originally designed for a vacuum return" you may take that as gospel.

Where are you located?

bigpete638

NY

bigpete638

im reluctant to leave an exact location. I’m hired on probation at the moment and don’t want to cause trouble.

neilc

for posting and studying here?
you ought get tenure, and a raise.

bigpete638

Lol im sure the establishment I’m working for would be subject to fines and or imprisonment had these conditions be publicly known.

retiredguy

I am new to this site and wish I had heard about it many years ago. Those vacuum return systems were common in the western half of Pennsylvania where the company I worked for was based. They were a fairly large rep and service company focusing on boilers of all sizes and capacities mostly for schools, hospitals and industry. The statements from the "pumpguy" are pretty much spot on so you can follow his lead. Also, if the system was engineered as a vacuum return system, you can not just shut off the vacuum and get good heating results. Many buildings and plants did it then complained about the poor performance. Trying to get these building managers to fix stuff was near impossible. I always loved going into a building with a well maintained steam system.

retiredguy

After looking at all the pictures you posted and the postings from everybody, I am going to guess that the return system has been disconnected and that all the return water is being routed to a drain or that red flash tank and then to a drain. My personnel experience is that any boiler that was subjected to all fresh water make-up, especially cast iron sectional boilers have a greatly reduced life. In most cases that I was involved in, the life of the boiler was reduced to 3-5 years. So all these owners of buildings and their managers that thought that they would save repair costs by dumping the return water were greatly surprised when they had to replace or repair the boilers after just a few years. Reconnecting that vacuum return tank is just the tip of the iceberg compared to all the probable repairs needed. Good luck--you are going to need it.

bigpete638

I’m actually working on 30 buildings receiving heat from a high pressure plant circulating high temp high pressure hot water. Each building has heat exchangers making low pressure steam.

bigpete638

It’s a disaster here and I’m going to need all the help I can get.

ratio

A water -> steam HX? Cool! Er, hot!

Pumpguy

@bigpete638, based on your comment about a 30 buildings system, and steam being generated from HTHW, I assume the HTHW is coming from a central boiler plant.

In this scenario, it is common for the condensate to just be dumped to the sewer, and the heat carrying fluid is just once through with nothing being returned.

In such a system, the goal is to wring every possible BTU from the steam before dumping the condensate to drain. It is usually recommend that the steam for building heat be as low as possible, and a good vacuum be applied to the return lines.

In addition, a condensate cooler is frequently fitted to reduce the sewer effluent temperature. This cooler is frequently fitted to the downstream side of the removal pump.

The preferred location for the condensate cooler is on the upstream side of the vacuum pump. This cooled condensate contributes to the life and pumping capacity of the vacuum pump. The condensate cooler can be used to preheat DHW, so the condensate heat is put to work and not wasted.

The attached file addresses the subject of condensate coolers in great detail.

retiredguy

@bigpete638, I heard about this type of heating system many years ago but have never actually seen one . The system I was told about was being installed somewhere in western N.Y. The high temp water was a by-product of some type of operation or manufacturing process. They have to cool the water, so selling it for heat production was a plus for them. You said that your buildings use this high temp water to produce steam. If you are paying for the use of the hot water, having an efficient steam heating system on your end may help save the buildings operating budget. Finding out how you are paying for the use of this hot water could direct you to the best plan for maintaining the heating systems and give insight to any repairs that should be made. Without knowing more about your particular systems and how they operate, giving any recommendations on how to proceed with any update or maintenance procedure on our end would just be a "shot in the dark". When I was still working, this would have been a great project

bigpete638

I have to remind myself to check this website. Thank you again for all the info.
Is there a way to get email notifications when a reply is made here? Trying to figure it out.

ethicalpaul

Yes, you can click the star at the top of the thread and it will mark it as a favorite and then you will get notifications (at least I do)

ratio

If you go to your profile page, there's a 'notifications preferences' where you can turn on (or off) email & popup notifications for a number of different events.

bigpete638

Awesome! I pressed the star and it worked! I won’t miss notifications anymore

Erin Holohan Haskell

Thanks, guys. Here are some more tips @bigpete638 https://heatinghelp.com/forum-user-manual

Harry_6

Greetings. Fascinating discussion/situation. I've worked with vacuum systems for several decades, and thought I might mention (since I haven't seen it addressed) that there is a common misconception that the vacuum somehow is used to "suck" water from the returns, when this is almost never the case.

In almost all case the returns are designed to return the condensate by gravity to the condensate/vacuum pump receiver. The air travels through the condensate return main along with the condensate. Typically, one only has to keep the return from forming water seals (like dropping the pipe and then having it rise up again - thus trapping water and preventing air flow) so the air can be extracted from the system, and all is well.

In some fewer cases, where the condensate return is below the pump, a special "vacuum return" or "lift" fitting is located at the vacuum pump which siphons the return water and sucks gulps of air into the pump, but these are not too common.

As was said earlier, the condensate and air return line goes into the pump at the strainer where the compound gauge and condensate thermometer are located. There is a vent on the tank top. There should only be the inlet line, the pump discharge and that vent (which may be a check, if I recall). There should be no open pipes on the tank. I think it's a Hoffman VLR, or similar, if memory serves. Those pumps use a Venturi on the pump discharge to create vacuum. Live steam getting into the pump will destroy the vacuum (and eventually the pump).

In systems where the boiler pressure, or close to it, is being used throughout the system, the boiler would also be under vacuum. In systems where the boiler pressure is being regulated down by a PRV, on the low side of the PRV is where the vacuum stops.

There isn't the space to go into all the advantages of vacuum systems - that's why everyone used (and still use) them. But . . .(1) Maintaining the returns below atmospheric pressure allows them to fill much faster when the steam is filling them. (2) The pipes could be smaller because of this. (3) When one has control of the vacuum one can control the temperature of the steam to suite one's needs. In a commercial or residential setting that means that as the weather becomes more moderate, the vacuum can be increased and the steam supply throttled, allowing for steam at temperatures as low as around 180 degrees - the same as hot water. (4) And lower pressure being carried means lower fuel costs.

Yep, vacuum systems are the cat's meow, but you have to maintain your traps to keep steam from leaking into the returns. That's why there's a thermometer at the return strainer. A little is OK, but live steam'll eventually chew that poor pump up. I've seen pumps where the engineer constantly had a garden hose pouring over the receiver to try to minimize the damage! And once the traps are pretty good, you go around and repack valves wherever you think they might leak.

Judging by the photos, the system operating as designed might be a long way off. Especially when owners are cheap. At my old employers we had a saying about the company philosophy: "Spend whatever it takes to save a dollar."

bigpete638

I wish my employer had the same philosophy.

Pumpguy

@Harry_6, Well said, well said!

The only comment I can add is that a lift fitting should never be used at the end of the low return just before the vacuum pump's receiver tank inlet. Proper piping calls for an auxiliary accumulator tank with float switch to control the vacuum pump.

If the low return is fitted with just a lift fitting, the vacuum pump will have to run continuous to keep the low returns drained of condensate.

When the vacuum pump shuts off due to a satisfied vacuum switch, the condensate accumulates in the low returns, forming a water seal which prevents any venting from occurring. This is due to an equalized pressure between the low returns and the vacuum pump's receiver tank.

If long enough, the low return could hold up a considerable amount of condensate, causing a flood condition when the vacuum pump comes on again. Remember, all fluids flow from high pressure to low pressure, always.

With an auxiliary accumulator tank, the vacuum pump can run start - stop, controlled by the float switch on the auxiliary accumulator tank.

For control wiring, the vacuum switch is wired in parallel with the auxiliary accumulator tank's float switch, so when either switch's contacts close, the vacuum pump operates.

The attached file goes into great detail on this subject.