A gallery of home built hoods and fume scrubbers _hood_

[geoffrod]

You will be much better off using an e-ductor driven by water.
If gases comes through they will be dragged in with the water.
Use a tank and an electric water pump to pump the water through the e-ductor.

Hi,
so the double diaphragm water pump i bought doesnt seem to be producing enough flow to make the eductor work very well.
I attached the eductor to the mains water and got a nice suction thru the eductor, so back to the drawing board. need to find a better pump.
Edit - i have bit the bullet and purchased this pump.
after testing with the hose i asked Copilot and they did some calculations for me - i think this pump should provide similar specs on delivery.

1. Calculate the flow rate per second:

Flow rate per second=20 liters50 seconds=0.4 liters per second\text{Flow rate per second} = \frac{20 \text{ liters}}{50 \text{ seconds}} = 0.4 \text{ liters per second}

1. Convert the flow rate to liters per minute:

Flow rate per minute=0.4 liters per second×60 seconds per minute=24 liters per minute\text{Flow rate per minute} = 0.4 \text{ liters per second} \times 60 \text{ seconds per minute} = 24 \text{ liters per minute}
So, your water supply delivers 24 liters per minute.
In New South Wales, the standard mains water pressure for residential homes typically ranges between 300 and 500 kilopascals (kPa), which is approximately 43 to 72 pounds per square inch (psi)

 

[4metals]

Seeing as you will be using an eductor to draw fumes through a scrubber and transfer liquids that tend to fume, selecting a pump that has corrosion resistance will extend it's life. The liquid you will recirculate tends to become corrosive and takes its toll on the pump.

 

[geoffrod]

Seeing as you will be using an eductor to draw fumes through a scrubber and transfer liquids that tend to fume, selecting a pump that has corrosion resistance will extend it's life. The liquid you will recirculate tends to become corrosive and takes its toll on the pump.

Thanks for the reply @4metals greatly appreciated. will careful monitoring of the fluid running thru the pump help improve the pumps longevity?
btw, thanks for all the great information on this subject that you have provided.
Regards
Geoff

 

[4metals]

will careful monitoring of the fluid running thru the pump help improve the pumps longevity?

Yes, if you monitor the pH and keep it neutral [ish], using caustic you can extend the life for sure. I live in the real world of refiners who only maintain stuff when it breaks. For them I recommend using the March series of highly corrosive magnetic drive pumps HERE. I always visit refineries, or I did before I retired, with 2 things, pH papers and a dropper bottle of stannous chloride. The pH papers to check the pH of their vacuum reservoir to judge just how often they do not do maintenance, and the stannous to drip on the floor and trash can contents to see just how sloppy their workers are. I don't hide what I'm doing because hopefully they will learn to do it themselves to see how their staff is actually performing. (one can hope right?)

 

[4metals]

I always visit refineries, or I did before I retired, with 2 things,

Actually with 3 things. I have a very accurate pocket velometer to roughly gauge the air velocity through the hoods, another thing to keep tabs on.

 

[geoffrod]

Yes, if you monitor the pH and keep it neutral [ish], using caustic you can extend the life for sure. I live in the real world of refiners who only maintain stuff when it breaks. For them I recommend using the March series of highly corrosive magnetic drive pumps HERE. I always visit refineries, or I did before I retired, with 2 things, pH papers and a dropper bottle of stannous chloride. The pH papers to check the pH of their vacuum reservoir to judge just how often they do not do maintenance, and the stannous to drip on the floor and trash can contents to see just how sloppy their workers are. I don't hide what I'm doing because hopefully they will learn to do it themselves to see how their staff is actually performing. (one can hope right?)

So am i too assume that the starting pH is neutral water? i was thinking i would use sodium carbonate mixture keeping it high? in the canisters i was going to use sodium hydroxide in the last 2 and water and peroxide mix in the first?

I thought i had read that you mentioned that this type of scrubber will only scrub 80% of the fumes? would it then be a benefit to recirculate the fumes back thru a second scrubber and therefore scrub 80% of the residual 20% from the first scrub? which should leave about 4% un-scrubbed?

 

[4metals]

I thought i had read that you mentioned that this type of scrubber will only scrub 80% of the fumes?

Lots of scrubber designs have been discussed here, which are you planning on building?

 

[geoffrod]

Lots of scrubber designs have been discussed here, which are you planning on building?

the one that you have presented here.
i have the fan and venturi working for the hood extraction, i have 3 canisters completed, i am now working on the water aspirator vacuum system.
I have another question in regards to the return water thru the Eductor/Aspirator, you have indicated that it should go into a return tune in the reservoir, but how does this work, does the tube have holes in the base or all over it, is it blanked off so as to send the return water out of it and over the top?
Thanks in advance

 

[Yggdrasil]

the one that you have presented here.
i have the fan and venturi working for the hood extraction, i have 3 canisters completed, i am now working on the water aspirator vacuum system.
I have another question in regards to the return water thru the Eductor/Aspirator, you have indicated that it should go into a return tune in the reservoir, but how does this work, does the tube have holes in the base or all over it, is it blanked off so as to send the return water out of it and over the top?
Thanks in advance
View attachment 67113

The water goes through the e-ductor and directly into the tank as a reservoir.
The pump then pumps from the same reservoir.
Over time the water in the tank may go acidic so a mild caustic solution is good to have.
Test it from time to time and if it creeps towards 7 add some more carbonate.

 

[4metals]

With a 10 cfm venturi and 3 tubes 48" long and 6" diameter you should achieve good fume scrubbing efficiency and the pH in the reservoir will be influenced by any inefficiency of the scrubbing. Keep the water as neutral as practical and put a pound or 2 of marble chips in the bottom of the reservoir to help buffer the pH.

The tube is because the venturi will spit all of the scrubbed air into the reservoir which includes a lot of bubbles. What can happen is the intake to the pump may suck in air if you do not redirect those bubbles. If that happens the pump will run in cavitation and stop pumping. The pipe simply re-directs the bubbles upward and the water flows out under the pipe which is not attached to the bottom, it just sits there. You can add a few holes towards the top in case your reservoir water level gets low but the concept is simply to redirect upward the air entrained by the venturi.

 

[geoffrod]

With a 10 cfm venturi and 3 tubes 36" long and 4" diameter you should achieve good fume scrubbing efficiency and the pH in the reservoir will be influenced by any inefficiency of the scrubbing. Keep the water as neutral as practical and put a pound or 2 of marble chips in the bottom of the reservoir to help buffer the pH.

The tube is because the venturi will spit all of the scrubbed air into the reservoir which includes a lot of bubbles. What can happen is the intake to the pump may suck in air if you do not redirect those bubbles. If that happens the pump will run in cavitation and stop pumping. The pipe simply re-directs the bubbles upward and the water flows out under the pipe which is not attached to the bottom, it just sits there. You can add a few holes towards the top in case your reservoir water level gets low but the concept is simply to redirect upward the air entrained by the venturi.

Ah got it, thanks for the detailed explanation.
so marble chips you mean calcium carbonate?

 

[4metals]

Yes here in the states garden centers sell bags of chipped marble, small stones crushed into gravel size, for use in gardens or ponds. Marble is calcium carbonate and the larger pebble size will slow any dissolution.

 

[geoffrod]

Yes here in the states garden centers sell bags of chipped marble, small stones crushed into gravel size, for use in gardens or ponds. Marble is calcium carbonate and the larger pebble size will slow any dissolution.

I couldnt get marble chips, but i found the pet place down the road is using decomposing coral for that same purpose in his fish tanks. so i got some of it

 

[4metals]

I couldnt get marble chips, but i found the pet place down the road is using decomposing coral for that same purpose in his fish tanks. so i got some of it

New South Wales, Australia, coral makes sense.

 

[geoffrod]

So a bit of an update
I have a 170 litre drum, fitted a plywood platform to the bottom by cutting a hole in the plywood and slipping the barrel thru, then attached struts to the platform which are then attached to the upper retaining ring (plywood)
the new pump was fitted to the platform and plumbed into the bottom drum bulkhead fitting. from the outlet of the pump we run to the venturi fitting then the water returns to the drum thru a 20mm pipe standoff which sits inside a loose DN40 pvc pipe, video shows the pump working and i attached a vacuum gauge to it to measure the strength of the suction, not quite 10 InHg vac, im not too sure if this is relevant or not and would appreciate if those cleaver people here could enlighten me as to whether this will be what is required to draw fumes from a single 2000ml reaction beaker thru my wet scrubber.
cheers
Geoff

 

[geoffrod]

@4metals, i wonder if you could elaborate on this photo.
What is the cap made from please.
Kind Regards
Geoff

 

[Yggdrasil]

@4metals, i wonder if you could elaborate on this photo.
What is the cap made from please.
Kind Regards
Geoff

It do not need to be this fancy.
An inverted funnel i bit wider than the beaker will do.

 

[geoffrod]

It do not need to be this fancy.
An inverted funnel i bit wider than the beaker will do.

yes i have those coming, but was worried about the suction from the water aspirator being strong enough to get all the fumes.
BTW i hooked the water aspirator up to 1 of my scrubber canisters and can here the fluid inside bubbling so i assume it is working.

 

[Yggdrasil]

yes i have those coming, but was worried about the suction from the water aspirator being strong enough to get all the fumes.
BTW i hooked the water aspirator up to 1 of my scrubber canisters and can here the fluid inside bubbling so i assume it is working.

It is important the there is a flow so it need to be slightly open in the reaction end.

Edit due to cell phone writing.

 

[geoffrod]

It is important the there is a flow so it need top be slightly open in the reaction end.

Ok i understand, if i stick a cap in the beaker and it seals i wont moove anything. thanks for the clarification @Yggdrasil