DIY Vacuum Degasser

[Travellingwave]

I recently installed an Axionoma heat meter to our Mitsubishi 14kw heat pump. I has been giving useful info but like many others I have suffered problems with air in the system during the hot water cycle. I tried the various methods discussed in the topic about removing air, these have given temporary relief but the issue reappears after a while.

I had a look at various devices for removing air - the gold standard appears to be vacuum degassing but these units are very expensive (c £4000) and generally only used in commercial applications. So I thought why not have a go at making one!! how hard can it be?

I took some inspiration from the spirotherm vacuum degasser - whilst very expensive it is in principle quite simple - a batch of system water is fed into a vacuum vessel - a vacuum pump then pumps out the water feeding it back into the heating system , creating a vacuum so that entrained gas in released by the lowering in pressure(Henrys law), the vessel is then refilled and the released air is purged out from the top of the vessel.

I had a self priming pump laying about which I normally use for pumping water out of our well to fill the fishpond, this type of pump is available from a well known website for about £80. It claims a suction head of 8M (-800mBar vacuum) and delivery head of 46M (4.6 Bar) so capable of pulling a reasonable low vaccum and to pump water back into the heating system at 1.5 - 2 bar.

I have a flush/fill valve set in the heating circuit , one outlet feeds a 12v solenoid valve to control the inlet of water, this feeds into a T junction on outlet feeds a vertical piece of clear tube which forms the vacuum chamber, a non return valve is fitted to the top of the tube to allow for purging out air, The outlet of the T junction feeds the inlet to the pump, the outlet of the pump feeds water back to the heating system via a non return valve and back in via the fill flush valve. All made from standard plumbing fittings.

I have a level sensor at the top of the vacuum vessel to detect when it is filled with water, this is connected to an arduino uno , which controls the solenoid inlet valve with the following sequence

1. open solenoid valve
2. wait till level sensor detects water then close inlet valve
3. wait 6 seconds then repeat from step 1

The vacuum/water pump runs continuously, the flush/fill valves are adjusted so that the vacuum is filled at about twice the speed that the pump can empty it , in this manner when the solenoid opens the vacuum chamber fills till it is full (detected by the level sensor) , the pump then pumps away the water for 6 seconds , lowering the pressure in the vacuum chamber and releasing air from the water, after 6 seconds the inlet valve open letting in more water and the cycle repeats.

Photo Below

The contraption appears to work - and sucks out an amazing amount of air. I have used it in conjunction with a low pressure bake out (1 bar system pressure) I ran it for about an hour till the heat meter was happy even at 55 DegC - it was still pulling out air after an hour. I calculated it would take about 4 hours to process the whol system volume - expect to have to have a few sessions.

I will see if I can upload of video oof it in operation.

I have lots of ideas how to improve it.

[Travellingwave]

Ideas to improve it

1. Make the vacuum chamber larger diameter = more water processed each cycle and larger surface area to disperse micro bubbles.
2. My fill flush is on the return , so not the hottest part of the system, better to connect to flow.
3. If you don’t have separate fill and flush valves then should be possible to use fill only valve , with the feed to and from the degassed teed together as close as possible to the fill valve.
4. Put a Willis heater in the inlet pipe , so water can be got nice and hot without thrashing the heatpump. Maybe some safety concerns?? PRV needed etc.

[Travellingwave]

I put a video on YouTube

[Robert.Wall]

Please upload the video here, for the reasons we set out in the FAQ.

Thanks.

[Travellingwave]

Will upload video - I tried to but it is too big so will have to clip it down.

First hot water run this morning and no air detected by heat meter😀

[Travellingwave]

Here is short video

[Travellingwave]

Arduino code below

```
int step = 0;
int solenoid = 7; // inlet solenoid output
int level_sensor = 8; // level sensor input


void setup() {
  // put your setup code here, to run once:

pinMode(solenoid,OUTPUT);
pinMode(level_sensor,INPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  if (step ==0){
    digitalWrite(solenoid,HIGH); //open inlet solenoid
     step = 10;
     }
  if (step==10){
    if(digitalRead(level_sensor) == 1){   // wait for water to reach top of tube
      digitalWrite(solenoid,LOW);         // close inlet solenoid
      step = 30;}
}

  if (step==30){
  delay(6000);          // wait delay time for pump to empty tube
  step = 0;             // go back to start
  }
}

[Travellingwave]

Scematic Diagram

[Travellingwave]

Bill Of Materials

1 off Inlet Hose - Washing machine 3/4 inch BSP to 3/4 inch BSP - to suit your flush valve
1 off Inlet Valve - !2v solenoid valve - 3/4 inch BSP - 15mm pushfit - £6
2 off 15mm Female - 22mm Male reducer - £13
2 off 22mm - 1 inch BSP female coupler - £13
1 off 1 inch BSP Tee - Male-Female-Male - £13
1 off 1 inch BSP Male to 32mm MDPE coupler - £13
1 off 300mm long 32mm OD clear plastic tube - £ 9.79
1 off 1 inch BSP Male to 32mm MDPE 90 degree coupler - £7.50
2 off 15mm non return valve (single check valve) - £12
1 off self priming centrifugal pump -£89.99
1 off level probe (TOBEOME XKC Y25 well known website) - £8.84
1 off Arduino Uno - £16.74
1 off Arduino Uno Relay Shield - £7.99
1 off 12v wall plug
1 0ff 15mm copper tube

Total cost approx - £210

[Travellingwave]

Some further thoughts/watchouts

1. It is obviously important that all joints that are under vacuum are tight. I added a ball valve to allow the vent to be closed of, this allows me to fully pressure test the whole system by filling it with water at system pressure, I did have a couple of small leaks which will have been letting in air , the opposite to what is desired.

2. As less air is released from the water , the draw down in the tube gets shorter so less water is displaced each cycle, this will reduce the processing rate, it would be useful to add a valve to allow a bit of air to be added above the vacuum to give the pump more chance to pull down the water.

3. On a mk2 I would make the vacuum tube wider and longer and have the water entering half way up the tube to give more chance for air to get out before it is sucked into the pump.

[Travellingwave]

Just re-reading the thread about getting air out, in it there is a link to a document by IMI which is very informative. Looking at the graph below it would appear that if a vacuum of -500mbar can be created then running the degasser at 40deg C would remove sufficient air to prevent any bubble formation at 55 degc under normal system pressure of say 1.5 bar.

https://pirateheatingsupplies.com/wp-content/uploads/2024/08/mwphs-training-document-imi-air-problems-causes-technology.pdf

[Travellingwave]

So far my DHW runs have been air free😀 so it seems to have worked.

I have some more ideas for improving it , making it a continuous process rather than a batch process. So maybe a lot faster.

[Travellingwave]

Plan for MK2 version

Same bits - different order plus one additional solenoid valve.

Theory is pump runs continuously as before. System water is normally fed via a throttling valve such that pump is pulling a vacuum on its inlet. Water enters degassing chamber at the top and exits from the bottom - releasing air as it travels down. As air starts to collect at the top of the tube the water level in the tube will start to drop, when level sensor is uncovered both SV1 and SV2 open for a fixed time period, SV1 bypasses the throttle so that water in exceeds water out and the level in the tube will rise, air is expelled via SV1. After time period solenoid valves close and operation continues.

Benefit - continuous not batch so should be higher throughput

Guarantees a minimum flow through the pump can’t get vacuum locked like the mk1 version.

[Travellingwave]

Tube could also be inclined to help with air separation.

I will give it a go in next days.

[Travellingwave]

Looks like you can buy it ready made if you have a spare £1000.

https://pirateheatingsupplies.com/product/reflex-servitec-mini-vacuum-spray-tube-degasser-8835800/

[Travellingwave]

Uses a diaphragm pump rather than a centrifugal pump. These are also available relatively low cost, not sure what suction head they have . Much lower power consumption (60w is stated£

[Ringi]

With a list price of £1000 should be possible for a rental company to charge £200 per week.

[Travellingwave]

I imagine a bit niche for your average tool hire shop - how many people would know or care about micro bubbles in their heating system?

[Ringi]

Next day shipping would only be £10 each way, so don’t need to be local.

With UFH it can be hard to remove air, with radators I would just run at 65c for a bit while bleeding.

[Travellingwave]

Perhaps Pirate heating supplies could offer a hire service as well as sales.

I think the MK2 DIY version could be cobbled together by any competent DIYer - if arduino or other controls are not your thing you could just operate it manually, just let it run and switch the pump off once enough air has collected to bleed it off. So £150-200 for a pump and a few plumbing bits. It probably won’t get as much air out as a commercial unit, but seems to be good enough to allow the heat meter to work.

You can also do a pretty good job just with the pump and a bucket - effectively dropping to atmospheric pressure- see photo below of an earlier effort. My concern was with having lots of water spraying around when it’s been sat Luke warm in a low temp heating system (legionella risk??) but should be ok if a fresh fill.