Trouble with super vent

acandheat22

Has anyone had trouble with the bell and Gossett Supervent sucking in air and causing the baseboard to get air bound. Sucking in air and a positively charged system

Jamie Hall

Bell and Gosett? Supervent, so far as I know, is a trademark of Honeywell-Sparco…

In any case, the only way an air vent -- of any flavour -- can suck in air is if the pressure inside the pipe at the vent is below atmospheric. Check your cold and hot system pressure at the inlet to any circulating pumps.

acandheat22

Feed Is working fine, 15 psi in the boiler

Jamie Hall

acandheat22 said:

Feed Is working fine, 15 psi in the boiler

At the pump inlet? When the pump is running? And what is the elevation difference?

Ironman

In relationship to the boiler, where is the pump, the expansion tank connection, and the MBR? Pics or a diagram would help.

Boiler gauges are not always reliable.

Ironman

Also, are you assuming the MBR is sucking air in because you're getting air in the system? It's very unlikely, in fact almost impossible, if it's under positive pressure all the time. And there is a cap on top that can be close to confirm that.

hot_rod

It is possible to pull air into a hydronic system thru an auto float vent. The circ, pumping at the PONPC, low fill or a circ capable of that delta P. Here is a visual.

Also cavitation induced vapor pockets can be diagnosed as an air problem sometimes. Look for a a restricted valve or blockage in the piping.

Big Ed_4

By chance do you have heating pipes run under a slab ?

Jamie Hall

hot_rod said:

It is possible to pull air into a hydronic system thru an auto float vent. The circ, pumping at the PONPC, low fill or a circ capable of that delta P. Here is a visual.

Also cavitation induced vapor pockets can be diagnosed as an air problem sometimes. Look for a a restricted valve or blockage in the piping.

That's why I suggested checking the pressure at the pump intake...

mikeg2015

I’ve had the suction of pumps go below atmospheric even with 30psi of the discharge side. The OEM guys didn’t believe me. Had to take a video with me sticking my finger on the vent.

Solid_Fuel_Man

@mikeg2015 on that system, where were the circulators, and we'd here was the expansion tank, also where was the vent located? I bet we can guess the answers!

mikeg2015

It was a multistack (multijunk) reverse cycle chiller with variable flow primary. It was piped reverse return with an end loop bypass to maintain minimum flow rates with horrific control characteristics and tuning. The tail wag wagging the dogs and the pump speeds and bypass valve were fighting each other.

Imagine driving a car and the driver has the throttle and you tell him ot keep it at exactly 70mph, and the passenger has the brakes and you tell them keep it at exactly 70mph.

It was stupid. Should of had 2 sets of pumps instead pumping away from each other with a low loss heater. But a single valve is a lot cheaper.

The pumps pumped towards the chiller with expansion tank on the suction side. Pump as nearly dead headed but trying to run at full speed and achieve flow rate. As it started to cavitation, flow fell off so it then ramped up even faster.


To give you an idea of the quality of design and engineering on this thing. The mechanical contractor forgot ot change the control valve size when they upsized the largest air handler. Have a 2” valve and pipe, where they needed a 3”. Couldn’t get it to balance because balancing valve was too small. Their solution, install a 4” balancing valve (yes, one of those $900 valves) so we could basically leave it wide open. I tried ot explain to them that in a reverse return with modulating control valves that control to discharge temp, it’s effectively self balancing, and to just get rid of the valve.... and that they wasted $10000 of balancing valves, the design, engineering and T&B for all of the valves plus the wasted pump energy.

They also installed a seperate lochinvar water heater when they had a Lochinvar FTXL boiler with DHW control built in sitting right next to it that was only used in the winter for backup heat. Could have saved $10k and installed a indirect.

Whole project is part of why I quit facilities management and corporate BS and went into the HVAC trade.

Solid_Fuel_Man

@mikeg2015 I COMPLETLY understand your sentiment. I've piped and controlled many many many large commercial projects with at least 1/3 of the materials could have been eliminated. Balance valves either all 25% open or all 100% open is a big red flag that they were not needed. I enjoy design-build jobs much better. I like to learn from my own mistakes (which I've made plenty).

Most of the time beautiful engineering is in the simplicity of a design which meets all the criteria of a spec.