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Vacuum Pump for Dehydrator
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I'm looking at getting a Welch 1402 Vacuum pump. Specs say 5.6 CFM / 1.0 x 10-4 Torr (29.92+ HG)

How do I know before purchasing that it will really pull the dehydrator I'm building down to 29 HG?

Can I just put a gauge on it?

This message has been edited. Last edited by: Diablo,
 
Location: NPR, Florida | Registered: January 29, 2010Reply With QuoteReport This Post
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I dont understand the question?
Are you asking how to tell what the vacuum pressure inside your vessel is? If so, than yes, put a vacuum gauge on the tank or on your collection container at the output of your condenser or wherever in the loop...
What type of pump is it?

Cheers,
Jon
 
Location: Wellington County, Ontario Canada | Registered: February 07, 2008Reply With QuoteReport This Post
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What I was asking is...I'm looking at buying a pump. Lets say pump is rated at 29 HG, but it is a used pump and no way to hook it up to any kind of a vessel to test.

So if it pulls 29 hg on a gauge, is it then likely to do same with vessel or is it possible that it won't? If it is possible that it won't could it be far off? Like gauge reads 29, but then vessel won't do better than 27 or something?

I just want to make sure I don't waste my money.
 
Location: NPR, Florida | Registered: January 29, 2010Reply With QuoteReport This Post
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I have a Welch here that was recommended for vacuum work by another biodieseler. Don't know the model, haven't unwrapped it yet.

If your pump won't pull 29" (and it's capable) then you have a leak somewhere, or else something is evaporating raising the vapour pressure inside your vessel. Which is pretty much what you want. You will only pull the hardest vacuum when everything has boiled off that can boil off.

Does that help? Google vapor pressure and partial vapor pressure, wikipedia is very helpful.

Jon should be able to tell you about the need for circulation when you're attempting to boil off water or methanol.
 
Location: New Zealand | Registered: August 15, 2006Reply With QuoteReport This Post
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Yep, what Paulus said.
You can hook a gauge to the pump before you buy it and that will tell you what its capable of.
When it comes to the vacuum plumbing on your condenser, recovery vessel and tank, use as large a pipe as you can afford as that will make a big difference in the speed at which you can dewater and recover methanol.
Cheers,
Jon
 
Location: Wellington County, Ontario Canada | Registered: February 07, 2008Reply With QuoteReport This Post
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quote:
Originally posted by Jon Heron:
Yep, what Paulus said.
You can hook a gauge to the pump before you buy it and that will tell you what its capable of.
When it comes to the vacuum plumbing on your condenser, recovery vessel and tank, use as large a pipe as you can afford as that will make a big difference in the speed at which you can dewater and recover methanol.
Cheers,
Jon


I assume you are talking about the copper coil between the main tank and condenser, as it's a cost variable? I was going to use 3/4.

The plans don't call for copper from condenser to recovery tank(s).

Should I go larger?

What are you running?

Also, do you chill your water or use any form of anti-freeze solution? If you do, can you elaborate on it? I'm in FL, so it's going to be warm most of the year.
 
Location: NPR, Florida | Registered: January 29, 2010Reply With QuoteReport This Post



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The entire bit of vacuum piping from the pump input to the tank output is what I am referring to. I am not sure which copper coil your talking about.
3/4" would be much better then the 3/8" I used, I hope to swap it out for 5/8" in the spring.
While operating under vacuum the larger the pipe the quicker you can recover, up to the capacity of your pump (CFM) and boiler (BTU).
I used 3/8" copper pipe for my condenser and its too small. When I start recovery the expansion of methanol vapours actually pressurizes the reactor tank for the first 8~10 hours, even though the gauge on the recovery vessel is at 29Hg, its because the 3/8" pipe is too small and too long to keep up with the rate of methanol evaporating.
So use as big a pipe as you can afford for the entire vacuum system including the condenser to get the most efficient vacuum operation.
I used to use a medium sized chest freezer full of glycerine and water as the antifreeze, that worked exceptionally!
On my new big setup I had a problem with the antifreeze pump on my first batch and switched to the garden hose to get it done. I still haven't got around to setting up the antifreeze freezer again, but I do plan on it as it wastes a lot less water. I also recommend running your cooling line around your recovery tank, the colder the tank the less vapours go through your vac pump. I used 1/2" pex piping and held it in place with pallet wrap before insulating it with bubble wrap.
Cheers,
Jon
 
Location: Wellington County, Ontario Canada | Registered: February 07, 2008Reply With QuoteReport This Post
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What pump did you use to circulate the anti-freeze?

How fast do you pump it?

Did you actually plumb intake and discharge lines into the freezer?

Never would of thought of a freezer chest.

I found a 25 cu ft (187 gallons) for free on craigslist, needs charged.

This message has been edited. Last edited by: Diablo,
 
Location: NPR, Florida | Registered: January 29, 2010Reply With QuoteReport This Post
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Diablo, If it needs charging, it probably has a leak, so get that repaired first before charging. Jim.
 
Location: Cape Town | Registered: May 17, 2006Reply With QuoteReport This Post
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quote:
Originally posted by Jon Heron:
I used to use a medium sized chest freezer full of glycerine and water as the antifreeze, that worked exceptionally!


Did you get that from me?

I have a couple dozen customers in hot climates that I've told to do exactly this.. The thing is, its not a cure-all for production purposes. The amount of heat being extracted from the dehydrator is far greater than the amount of heat extraction capacity of the freezer.. So, the freezer ends up acting sort of like a thermal battery.. When you go home for the day, it works continuously to drop the temperature of the antifreeze for the next day (a charge).. But that charge has its limits.

In short, a freezer will improve your processing if your processing is limited.. but in a production environment, you're going to need a real chiller to keep up.

Hope that helps,


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Registered: March 09, 2006Reply With QuoteReport This Post
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How do you size a chiller?
 
Location: NPR, Florida | Registered: January 29, 2010Reply With QuoteReport This Post
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Hi Murphy,
I guess great minds think alike! Wink
I came up with that on my own, I posted about the setup here 4 or 5 years ago I think...
I am not in a production setup and only brewed on the weekends, it sure worked well for that but I doubt it would ever keep up in a production environment, with the tiny compressor thats found in your typical chest freezer.
Diablo,
I used a harbour fright style regenerative turbine pump for the antifreeze.
I cut holes in the lid of the freezer for the in out pipes, I had it about 3/4 full.
I pumped it full speed through my old plumbers delight condenser (1/2" copper inside of a 3/4" copper sleeve) It would make frost on the outside of the condenser jacket when it was 40C in the processor shed!
To properly size a chiller you need to know the input energy, energy consumed by the evaporation of the product and the volume, then its just a mathematical formula as I understand it...
Cheers,
Jon
 
Location: Wellington County, Ontario Canada | Registered: February 07, 2008Reply With QuoteReport This Post



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