Positive air pressure for van

Submitted: Monday, Feb 01, 2021 at 06:48
ThreadID: 141028 Views:1401 Replies:7 FollowUps:7
Hi I have purchased a continuous cycle Bilge Blower and bilge blower hose to try and create positive air pressure in my caravan to minimise or eliminate dust ingress. When id did some testing with the bilge blower hose attached I found it greatly reduced the amount of air flow from the blower. I am now concerned that when I connect an air filter as well the unit will not create enough air flow to create positive air pressure.
I know there are commercially available products such as the Carafan, these are out of my current budget.
I do not want to fit a forward facing snorkel on the van, I was planning to pull air in from a vent located high on the right hand side of the van.
Just concerned about the loss of air flow with the blower just connected to the hose.
Any suggestions or ideas on how to overcome this problem?
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Reply By: Member - John - Monday, Feb 01, 2021 at 08:11

Monday, Feb 01, 2021 at 08:11
How long is the hose you attached? Is it the same length as you require in the final location?
AnswerID: 634926

Follow Up By: Daniel G3 - Monday, Feb 01, 2021 at 09:38

Monday, Feb 01, 2021 at 09:38
Hi John
The hose length is 3 metres but has wire wrapped around it to keep the 75mm open. I will cut it to the desired length and see if this makes a difference. My other concern is once an air filter is connected it will restrict the air flow even more.
I cut the hose into a 300mm length and it still affected the blowers output. I may have to look at a larger hose to feed the blower
FollowupID: 912351

Reply By: Erad - Monday, Feb 01, 2021 at 08:32

Monday, Feb 01, 2021 at 08:32
Without knowing the details of the fan, it is possible that the bilge fan may be appropriate for your usage. However, centrifugal fans have a relatively low range of operation before the fan vanes stall and then they don't pump very much air. Because the airflow has dropped, you will hopefully have an increase in pressure at the fan exit, which is exactly what you are after. Note that the fan will not work if you have the other vents open to the air because all the air you blow into the van will be lost. We have a small piece of carpet underlay which we use to block off the lower vent in the 2 part door. We insert it when we are going to drive on a dusty road and it stops 95% of the dust entering the caravan. BUT _ it is vital that you take it out when you are not travelling because that lower vent is there to allow any gas which leaks from the fridge or the stove to escape from the van.
AnswerID: 634927

Follow Up By: Daniel G3 - Monday, Feb 01, 2021 at 09:42

Monday, Feb 01, 2021 at 09:42
Hi Erad
The blower is a Rule 75mm which specifies 135 cu of air. It works very well without the hose attached. Again I have real concerns about how much more restriction will be introduced once an air filter is incorporated.
I have not permanatley attached the fan as I was testing to see if it was adequate.
I did put plugs in sinks and shower, Blocked the door vent but when I used the blower with the blower hose the pressure output dropped substantially
FollowupID: 912352

Reply By: Peter_n_Margaret - Monday, Feb 01, 2021 at 09:56

Monday, Feb 01, 2021 at 09:56
"I do not want to fit a forward facing snorkel on the van,"
Does not need to be a "snorkel", just a forward facing vent, no fan and no filter, just some S/S fly wire to keep bugs out. Just needs to be configured to avoid water ingress.
The airflow is minimal if you have successfully sealed the van up, which is an essential starting point, in fact if the van is 100% sealed (which is not possible), there will be no airflow at all.
This works a treat. The outlet to the inside is higher than the intake and it also serves as the required top vent for gas.

OKA196 motorhome
AnswerID: 634929

Follow Up By: Daniel G3 - Monday, Feb 01, 2021 at 13:14

Monday, Feb 01, 2021 at 13:14
Thanks for the information Peter and I have no doubt that that system would work well on your vehicle.
My caravan is towed behind a Ford Ranger and I do have a stone stomper fitted which does minimise some dust. I am concerned that a scupper may still allow dust in. Adding some form of filter even if it is a washing up sponge will minimise the amount of air that gets inside the van.
Thanks for your response
FollowupID: 912353

Follow Up By: Peter_n_Margaret - Monday, Feb 01, 2021 at 13:46

Monday, Feb 01, 2021 at 13:46
I think you will find that the volume of dust at the top front of the van is minimal and as I suggested, the actual air flow is minimal. It is about making sure that those tiny little leaks that you can not find to seal are leaking out, not in.
OKA196 motorhome
FollowupID: 912354

Reply By: Notso - Monday, Feb 01, 2021 at 11:32

Monday, Feb 01, 2021 at 11:32
I've only ever used one of these.

https://www.caravansplus.com.au/scupper-vent-aluminium-240-x-150mm-white-p-497.html. Travelled heaps of dirt track with the van and dust was never a problem!

You can close it as necessary. Works well. Above all else don't block your vents as it's too easy to forget you've done it and you can end up sick or worse!
AnswerID: 634930

Reply By: Darian - Monday, Feb 01, 2021 at 14:02

Monday, Feb 01, 2021 at 14:02
If you check all of your vans door/window/hatch seals, plus fit a temporary lower door vent cover*, a modest inward air pressure will do the trick.
I chose to fit a Camec scoop over the original factory fitted scupper on the roof’s leading edge...the scoop and the scupper are a ‘system’...they mate, when the scupper is opened, but allow flow through when the scupper is closed...works a treat for inward pressure...and as a result, no dust at all.
*my temporary lower door vent cover has a red flag attached that sticks out of the door frame, as a reminder.
AnswerID: 634932

Follow Up By: Daniel G3 - Monday, Feb 01, 2021 at 16:35

Monday, Feb 01, 2021 at 16:35
Hi Darian
Thanks for the reply I will consider a scupper but would also like to progress with the Bilge blower if I can get it to operate correctly. Just concerned if I purchase a Donaldson filter at $300 and the blower fails to produce enough airflow to create the positive air pressure. Perhaps a combination of the two products will give the best protection from dust ingress
FollowupID: 912356

Follow Up By: Bob Y. - Qld - Tuesday, Feb 02, 2021 at 06:45

Tuesday, Feb 02, 2021 at 06:45

Unless the fitting of a Donaldson filter suits your planned design, it seems a big expense for what will be not a lot of dust anyway. You could peruse the filter aisle at Supercheap, and find a suitable flat filter element you could fit to an inlet vent.


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FollowupID: 912361

Follow Up By: Daniel G3 - Tuesday, Feb 02, 2021 at 07:13

Tuesday, Feb 02, 2021 at 07:13
Thanks Bob that is a great suggestion. Certainly cheaper than the Donaldson unit and if it does not work then I have not wasted a lot of money.
FollowupID: 912362

Reply By: Member - John - Monday, Feb 01, 2021 at 19:14

Monday, Feb 01, 2021 at 19:14
Daniel, Is the hose convoluted hose? If so, try and get smooth hose or PVC, much better air flow. Again good luck.
AnswerID: 634934

Reply By: Erad - Tuesday, Feb 02, 2021 at 18:30

Tuesday, Feb 02, 2021 at 18:30
A scupper vent in the caravan roof works quite well, although being forward facing, if it rains, ..... As for dust entry via the scupper or your bilge fan, you can buy some filter media from an air conditioner supplier and jam it in the intake. We do this with our scupper vent and it works very well, although at roof level, there isn't very much dust anyway.

Our first trip with our poptop van was a disaster. No foam blocking the lower vent in the door, and the dust was at least 1 cm think. The next trip was to Tiboorburra via Gladstone in Qld (heading west then south then west etc). After Nocundra, there were places where I couldn't even see the caravan - the dust was so thick, yet with just the foam in the door, there was very little dust inside the van. That was with no scupper vent in the roof at that time. Subsequently we fitted the vent in the roof and it works well.
AnswerID: 634948

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