Ok, many people use (or recommend) the use of a Harbor Freight Clearwater Pump (designed for pumping water) for use with pumping oil in a biodiesel processor.
A recent fire has highlighted some potential problems with the pump.
I suppose my first question is how and why should a closed system catch fire because of a pump (motor) failure.
The oil should stay in the processor and the pipes, and there should not be an oxidizer in contact with the oil.
I'm thinking this reduces to a few issues with the pump.
The basic compact all-in-one pump/motor (this has PTFE (Teflon) rollers):
And the motor with a long shaft and separate pump head (rotary gear):
Both Grainger pumps list Viton Seals and Viton O-Rings.
However if heating of the armature and pump seals is the direct cause of the failure, perhaps one should choose a belt driven or chain driven pump that would do a better job at isolating the pump head from the motor.
---- Clifford ----
How about using a high volume pump (relative to batch size) that doesn't run for hours on end. Mine moves about 75GPM, 90 gallon batches mixing for about 30 minutes, 45 minutes max and never gets near hot. The 2hp motor is attached to the pump by a Lovejoy coupling.
Another option is to use an eductor or nozzle, really anything that can help reduce processing times so that there is less chance of the process being unattended could be beneficial.
The modified gear-type engine oil pump that DCS developed for collecting used VO would probably be perfect for this application, and inexpensive too.
Centrifugal pumps would in most cases be unsuitable. Positive displacement pumps are much better.
I am interested to understand the reasons why you would say a "centrifugal pump is in most cases unsuitable" when a "PD pump would be much better".
That has certainly not been my experience of this type of application so I am interested in the background and or supporting information to your comment.
Centrifugal pumps rely on accelerating the fluid to a high speed to induce a pressure in the casing. Viscous materials are much harder to accelerate than thin fluids like water so cavitation can be a real problem at the speed required.
The heat within the pump is greater because of the reduced flow and the poor heat transfer of oil. The high speed also means that something that can generate friction which includes the oil, can get very hot very quickly.
Another issue is back pressure, it is a real killer of centrifugal pumps, as the volume increases the back pressure increases even short lengths of small diameter pipe, bends and valves all increase the back pressure which reduces the flow.
None of these problems with the exception of some vane and helical screw pumps exist in most positive displacement pumps.
Cars use centrifugal pumps for cooling and washing the windscreen and maybe even your turbo and air horns. Oil pumps are all positive displacement because of the viscosity of oil.
Thanks Sinbad for the explanation.
I was wondering if there could be issues with using "clearwater" pumps for fluids that were far more viscous than the fluids they were designed to pump.
Although they should be designed to take some back pressure from high lift, or running an irrigation system. The HF pump is rated for 115 feet of lift.
I mean no disrespect but a few of these statements need correcting. Centrifugal pumps rely on centrifugal force to move fluids, not high speed.
In your defense however, I can certainly understand how it would seem to the casual observer that high speeds are the primary driver of a centrifugal type pump.
Your comments about cavitation are also wrong but that would be a length discussion. To shorten things, if the viscosity of the oil makes it so hard to move, how is it that it can be moved so fast as to cause cavitation?
A gear pump can create the same cavitation just as easily.
Specific gravity has more to do with the amount of energy required to accelerate the fluid than viscosity does.
Again, I can certainly understand how one could think that way however.
Another correction if you don't mind.
The heat within the pump will stay the same to all practical means of measuring so long as a very small minimum flow through the pump is maintained.
You are correct that the friction created by the spinning impeller can create heat but for our purposes of mixing biodiesel, this is actually a very good thing.
I would strongly caution that your statement of "get very hot very quickly" is also very misleading. You would have to completely block the pump discharge port (close the valve?) for the pump to build up any heat by way of friction. Even then, it would not happen quickly in our application. (and on that note, what would happen with a gear pump would probably be far worse)
In addition to that, and I would caution here that I have not actually done the math for this line of thought, but I do believe (educated guess), that a small harbor freight pump that is plumbed to steel pipes and with the discharge blocked, might produce such a small amount of friction heat that the mass of metal might be able to dissipate the thermal build up as quickly as it is generated.
Your comment about back pressure being a real killer is also very much incorrect. In fact, it is incorrect and misleading on so many levels I'm not going to even get into it.
Unless the pump and motor combo are specifically designed to run "open flow", almost all centrifugal pumps require back pressure.
Your comment about the pipe diameters, bends, lengths is correct but it certainly doesn't cause damage to the pump.
You want to bet on that? I'm sorry sir, with all due respect, from my perspective reading your statements, your understanding of pumps and fluid dynamics is flawed.
Oh come on! For crying out loud that's also misleading on so many levels.
Imagine what would happen to your engine if your thermostat stuck closed with a gear pump moving the coolant around. Not a pretty picture. Furthermore, imagine how big the gear type coolant pump would have to be to match the output volume of the centrifugal pump that's normally used.
Head on down inside the engine and imagine the engineering challenges created trying to use a centrifugal pump to send pressurized motor oil around all those tiny ports in your engines system.
I don't mean to be rude but your facts about pumping are not accurate.
If you want a really good biodiesel pump, go to my website and buy one.
Hope that helps and I sincerely apologize in advance if I offended you. My wife says I'm not the most diplomatic person in the world.
The best Do-it-Yourself Construction Plans on the Internet!
Waste Oil Heating - Biodiesel Systems
Biodiesel Pumps Made In The USA
Your wife must be nicer then mine, my wife tells me my poor diplomacy skills are due to a personality defect...
Simple schematic for a pump and heater control with a high limit
Sensor for the biodiesel/glycerin layer
No offense taken Murphy but you got me to google to check and I was wrong partly, but then so are you partly. According to Wiki
A centrifugal pump works by converting kinetic energy into potential energy measurable as static fluid pressure at the outlet of the pump. This action is described by Bernoulli's principle.
With the mechanical action of an electric motor or similar, the rotation of the pump impeller imparts kinetic energy to the fluid through centrifugal force. The fluid is drawn from the inlet piping into the impeller intake eye and is accelerated outwards through the impeller vanes to the volute and outlet piping.
If you check out the link above, scroll down to the problems with centrifugal pumps section where you will find a link on Cavitation
Part of it reads
At the point of total collapse, the temperature of the vapor within the bubble may be several thousand kelvin, and the pressure several hundred atmospheres.
2 thousand Kelvin is 3140f, and 100 atm is nearly 1500psi, Wow.
As Murphy has said so well above. You appear to have a complete missunderstanding of fluid dynamics and what happens in centrifugal and or PD pumps.
I don't think we need to say much more than Murphy has said in direct response to your comments but your original post appeared you where making a statement from a position of some authority and or experience which would have been taken as fact by others if not questioned, which is clearly not the case.
Yes, centrifugal pumps work on accelerating the fluid however that is not "high speed" as you stated. High Speed and acceleration are totally different things.
The conditions which cause cavitation in a centrifugal pump are just as likely to cause them in a PD pump. Also your "Wow" comment highlights your lack of understanding of what cavitation is an how it can be caused.
Do a bit of research into PSH and Vapor pressure rather than just a quick google/Wiki search. You will learn a lot about pumps.
I was a marine engineering mechanic in the RAN, lots of pumps, I never saw a centrifugal fuel/oil pump ever. But if someone can give me a link to such a pump that is not submersible I wont argue the point.
But I still wont use one, hot oil scares the crap out of me.
I don't think you understood what I was saying, the high speed I was referring to was the shaft speed, you know the motor speed which I assume is 3000rpm.
The acceleration was referring to the fluid traveling through the turbine and exiting at a much higher velocity due to the centrifugal force.
Has anybody ever bothered to check the pressures on the inlet and outlet at the pump on their system?
Your wife suffers from superior personality syndrom. What's wrong with straight forward in black and white ? Then you could always move to Quebec where everyone is diplomacy challenged
** Biodiesel Glycerine Soap - The Guide
- on 5 continents helping people make & sell soap from the Biodiesel Glycerine.
How many do you want and what do you mean by hot oil?
Hot oil to me in the edible oil and biodiesel industry is when it is being pumped around >200C. The temperatures required for oil drying and transesterification are not "hot oil" applications. They are pretty much standard duty for centrifugal pumps.
I appreciate that these are commerical pumps and not homebrew but they prove a point.
You asked for links and these are specific for hot cooking oil:
Also the last plant I worked on down your way the client purchased their hot oil pumps from an Australian company called Dickow: http://www.dickow-pumps.com/in...nd_gas/hot_oil_pump/
However there are thousands of applications where centrifugal pumps are used for "hot oils" heat transfer fluids are one and edible oil processing is another, including the production of biodiesel.The majority of edible oil in the supermarkets is more than likely pumped at >230C using a centrifugal pump during the deodoising process. Also biodiesel distillation is done at high temperature >200C and again mostly pumped using centrifugal pumps.
No, not all pumps run at 3000 rpm. We typically specify pumps to be normally four pole (1500rpm @50Hz or 1800rpm@60Hz) or even six pole which runs down at <1000rpm at 50Hz. However that is not due to the potential for cavitation it is more to reduce the shear effect. As far as cavitation, a propperly designed system with a corrrectly specified centrifugal pump will not cavitate even when the oil/ fuel is at high temperature. Get the conditions wrong and a PD pump will cavitate just as easily as a centrifugal pump.
Yes, why do you ask?
OK, so who's gonna call the Alaska pipe line guys and tell them they are using the wrong freakin pumps? http://www.alyeska-pipeline.co..._oil_pump_system.pdf
Don't be coy Fuzznag what sort of pressures are you getting with your properly designed correctly specified pump. Data like that could be used to compare the performance of the right pump against water pumps.
You are right there are centrifugal pumps out there designed to move hot oil. Everybody who uses a water pump should get one. They seem to have addressed the major problems, the magnetic drive eliminates leaks and some had water cooled bearings.
I forgot about shear, another reason not to use high speed turbines to move viscous material.The 1000rpm centrifugal pump you mention, what sort of impeller do they use, do you get much head at that speed?
And yes most if not all pumps can cause cavitation if not set up correctly, which is the point I was trying to make in the beginning.
Water pumps are not made to pump hot oil or methanol or deal with caustic substances. They are fine at doing what they were designed to do, pump water.
You can't turn a sows ear into a silk purse.
As far as cavitation, there have been experiments to create cavitation to improve the mixing of biodiesel, so it isn't all bad.
The issue is that the cavitation can cause premature wear on the pump and impellers which doesn't appear to be the major cause of pump failure in biodiesel production.
|Powered by Social Strata||Page 1 2|