Veggie lovers only - time taken to purge the filters, IP and lines - PeachParts Mercedes-Benz Forum

ah-kay · #1 02-02-2010, 12:31 PM

I am thinking of designing my own 2 tanks system - main tank is WVO and a small ( 1-2 gallons ) holding tank for diesel. I want to design a one shot electronic circuit to purge the lines from the holding tank at the end of the driving day. If I T the holding tank just before the primary filter, anyone has any idea how long it takes to purge the lines of WVO? I want to set up an one shot electronic timer to do that, assuming the car will be traveling at 30 mph or less during purging. I will press a button ( x sec/min ) before I park the car, lines will be purge with diesel and the car will start with diesel the next day. The only negative is that the WVO may not be at temperature when the diesel is used up in the lines at the next start but I will improve on that later.

John Schroader · #2 02-02-2010, 01:04 PM

Not exactly sure I'm following your logic, but here's my take. Run your car for a while and then park at idle. While running, disconnect (or turn off) fuel at tank. See how long it takes to die -- will run a while on fuel in filter, lines, etc. Of course now you are out of fuel and have all the associated problems with that to deal with before restarting. When I was building a two tank system for my old Powerstroke, I got pretty good at estimating how long it could run on fuel that was in the filter and lines. After I got the system built, I knew about how long to purge the lines before shutdown. Of course I alway purged them longer, just to be on the safe side. Trying to start on a cold day on WVO is not much fun.

Biodiesel300TD · #3 02-02-2010, 02:00 PM

At idle it takes 2-3 minutes to purge all the lines out, at 30pmh it will take maybe 1½mintes. Greaseworks sells a delay timer relay that allows you to set the close timing of the return valve. I have one in my 240. You can dial it from 1min - 5min. I have my system all on one switch. When I switch the VO off the supply valve is closed immediately but the delay timer relay continues to keep the return valve open for the set time length. I have mine set to 2.5 minutes. I also have the VO light in my dash hooked up to it so the light goes off when the shut-off closes. I've attached the flow chart for my VO system.

Here is a link to the delay valve - http://www.greaseworks.com/store/product_info.php?cPath=21&products_id=277

Also I highly suggest having separate filters for each fuel. This way you can always run diesel no matter what is going on with your VO filter. Usually the valves are wired with the normally open side to the diesel, and the switched open(normally closed) is the veggie oil.

ah-kay · #4 02-02-2010, 01:36 PM

Main tank -WVO, holding tank - Diesel.

T the feed just before the primary filter with a 3 way valve. Normally default to main WVO tank. On the way to stop the car for the night, I will press a button in the car and a timer will start. Valve is switched to diesel and the remaining WVO is used up in the IP, filter and hard lines. When I start the car the next day, car will start on and run on diesel for a short time ( whatever diesel is in IP, filter etc ) as the new feed is defaulted to WVO again. I just want to have an electronic circuit to do the timing for me but the timing does not need to be precise.

300dOwner · #5 02-02-2010, 01:54 PM

I'd be careful about utilizing a switch that defaults to WVO...likely better to do it the other way around, default to diesel and switch to WVO when operating temp / Veggie Oil temp has been reached. IMO the most elegant solution is to grab a co-pilot from grease car...I know there are many that maintain burning WVO wastes the engine, not going to debate that here..but you will potentially do a bunch of engine damage if you aren't careful about getting the oil hot enough and purging the system effectively. This also takes the oh crap i forgot factor out of it...

Other, manual solution, is to buy some dye at the local NAPA and time how long it takes to purge diesel at idle -- basically hit the purge circuit and look for the dye colored diesel coming back into the WVO tank

good luck with it..also make sure that you filter to 1 micron and dewater!

pselaphid · #6 02-02-2010, 02:00 PM

You need to rethink using the same filter for both fuels. It will take forever to purge your filter and rapidly deplete a small diesel tank. With separate filters on my vehicles it takes about 20 seconds, but requires a couple miles driving after line purge to burn up residual WVO in the IP. Ultimately you'll get a fuel mix with shared filters. I know this because on my first conversion I routed the fuel so that the main filter was shared, and I know I was getting fuel mixing fairly rapidly with frequent switching. I ran it like that for about 10k miles, then the car got hit and that was that, so I never found out if it had ill effects...engine worked fine and I still have it as a spare.

You didn't mention any heating system for the WVO, but presumably that's being worked up. Using the stock tank for WVO will result in polymerization problems. For the system to operate long term, you should just set up a proper dual tank system based on the many examples that are available. You might get better and/or more information, and may get less yelling, from one of the dedicated WVO discussion boards. I do appreciate you're trying to exclude the anti-WVO voices by your title, but they may nontheless infiltrate.

JEBalles · #7 02-02-2010, 04:08 PM

X3 on the separate filter. You didn't mention if you were heating the filter, which also prove to be problematic: cold weather, filter gets clogged with crystallized glycerol, and if it's heated, hot diesel, which starves the IP and injectors of proper lubrication, unless it's a switched electric heater.

Default should always be diesel. I know, I had a bunch of incompetent college students wire my system and I had to redo just about every connection cause the valves kept turning off spontaneously.

And on the topic of purging, I have a looped return which tees in right before the input valve and there's about 10 cm of hose between the 20 plate FPHE and the valve, so I only need to purge the VO up to the FPHE, not all the way back to the tank, right? How long would that take?

oldsinner111 · #8 02-02-2010, 05:33 PM

I take 10 miles to purge.I run in loop mode,then just switc supply from wvo to diesel.Never use Main tank for grease.Wvo interacts with metal tank creating the dreaded chicken skin.

BridelessRacing · #9 02-02-2010, 08:39 PM

I switch back to diesel within 3 miles of my house to purge usually 4 to 5 minutes

latitude500 · #10 02-08-2010, 06:00 PM

When I install grease kits for clients one of the last things you have to do is find out the purge time. This is the time for the diesel to make its way all the way back to the Veg tank. You do this by installing everything and simply setting it to purge when the engine is running. Then simple count how many seconds it takes until you see fuel going into the veg tanks. Every car and truck is going to be different. Even the same year and model is going to be different. Because you might have routed the fuel hose over the harness or under it last time. So it's not something you can guess on. You have to do it the hard way. Don't worry to much about the purge time anyways, just find out the time it takes to push diesel back to the veg tank, and drive a little longer then that. By the time you have everything pushed back. Everything will be out of the IP, and injector pumps and you will be buring diesel.

GregMN · #11 02-08-2010, 07:35 PM

If you share the filter, please understand that you cannot purge a filter body due to the way fluid passes through it.

To test this for yourself:
get a glass jar about the size of your filter body
put a input port toward the edge of the lid
put a output port in the center of the lid
fill the jar with dish washing soap
start a flow of water into the input port at the flow rate your car's fuel runs (1 quart/hr at idle, 1 gallon/hr at 30mph)
time how long it takes for the water coming out to no longer be soapy

gradyg3 · #12 02-08-2010, 08:46 PM

I agree every car is different in terms of purge times. A new VW tdi will purge in seconds, a older benz will take longer of course. Alos driving conditions will change purge times, driving up hill while accelerating will be much shorter purge than driving downhill coasting. One simple way is the sound and oil pressure test. I knwo that when warm on heated veg my car is much quieter and also the oil presure drops to about 1.5-1.75 at idle and when warm and on diesel, much more valve clatter, and also oil pressure usually right around 2. I use this as a general guide and also generally know where I need tostart the purge on my general commute routes. Good luck putting together your own two-tank, I tried to cost compare and greasecar.com system is hard to beat even if you build your own system, especially given the very sweet heated tank it comes with.

holtonmusicman · #13 02-10-2010, 04:44 PM

Greg,

Not to dispute your answer, just wondering aloud.

In your illustration you don't have a filter which would force the fluid in a specific direction (around the filter and through and out the middle) which would make a very big difference.

The soap idea also is not good. Using food coloring would be a better idea. I did that, and within 15 minutes (no filter) the water was clear. When I put a paper cup (holes stabbed into the sies) inside the same mason jar of water, with the blue food coloring, the cup acted like the paper filter would and that water cleared even faster.

If the filter were like the old gravity bowl glass filters we used on our tractor your theory seems to be correct, but maybe I'm missing something in the design? I've been running the same filter system (although I purge at least 10 minutes before I shut down on the way home) with no problems now for over 7,000 miles, in cold weather no less.

Again, if my experiment is flawed please explain it to me as I don't want to plug up anything (AGAIN).

thanks

GregMN · #14 02-10-2010, 05:49 PM

Quote:

Originally Posted by holtonmusicman

Using food coloring would be a better idea. I did that, and within 15 minutes (no filter) the water was clear. When I put a paper cup (holes stabbed into the sies) inside the same mason jar of water, with the blue food coloring, the cup acted like the paper filter would and that water cleared even faster.

You have sort of made my point. It takes a long time to purge an inline container. My 2 tank system purges the VO out of the fuel loop in 14 seconds, (fuel source valve, lift pump, IP, IP return & injector return lines, back to the fuel source valve). My point is that you will have VO sitting in the bottom of your filter while the diesel flows in and out the top part of the filter. As the filter media starts to clog, the pathway will move down the filter and you will start to suck the VO into the fuel stream. Note that old diesel Mercedes are very forgiving, but there is a limit.

If you are willing to put up with extremely long purge times, you will get most of it out. But, why drive 10 minutes on diesel when you can pull up to you destination and purge for a few seconds? My cost of a separate heated filter was $13 at a junkyard, plus the filter. http://members.fortunecity.com/greglyons/1991_MB_350SDL/1991_350_SDL_WVO_Conversion.htm

If you share an unheated filter the VO is going to cool down a lot.
If you share a heated filter you will be heating the diesel.

Cold VO causes problems in the cylinder by not spraying correctly, leading to carbon build up and stuck rings.
Hot diesel causes problems in the IP, hot diesel does not lubricate as well as needed and the IP will wear out.