Upgrading the Clearwater Pump for Biodiesel Processors
By Rick Da Tech
There are two pumps that are commonly used as biodiesel processor pumps. The NT Clear Water Pump has a long history of reliability when used as a biodiesel mixing pump. The less expensive Harbor Freight pump is considerably less reliable. For better or worse, homebrewing seems to be wedded to these pumps. You find them on nearly every set of processor plans and nearly every homebrew processor kit. They have two strong advantages of being inexpensive and extremely good at mixing. In fact they are so inexpensive that the pump industry classifies them as "disposable pumps" because they are not woth rebuilding.
More on Biodiesel Processor Pumps
Not all pumps of this style are disposable. The Italians at Pedrollo make a high quality version of this pump. It costs more, but it does not have any of the problems we find with the cheaper pumps. The Pedrollo Pump actually has real NPT pipe threads that seal. It also has thermal protection built into it. The capacitor is rugged enough to handle actual use without blowing. It is super easy to wire up, and is just plain made better than the Chineese versions.
They are called "regenerative turbine pumps" and are a variant of the common centrifugal pump. The common centrifugal pump feeds the input into the center of the pump. The liquid makes one pass through the blades and is output along the outer edge of the rotor blades. In the regenerative turbine pump, the liquid is fed to the edge of the pump and travels around the edge of the rotor blades in a special groove to the output port. As it travels around the pump, it passes through the blades many thousands of times, each pass building up a little more pressure on the output port. The result is a very high shear mixing pump. The flow is so turbulent that any trash will quickly damage the pump through pitting if using anything other than cast iron for the pump housing. The pump was designed specifically to trade off flow for increased head pressure. These pumps can build up to about 40 or 50 psi on the output. The American versions, designed for boilers are made with tighter tolerances and can typically build up over 250 psi.
The Harbor Freight pump uses a capacitor that is undersized, causing it to blow out easily. Neither pump has any thermal protection, meaning that if the pump locks up for whatever reason, it will over heat and possibly catch on fire.
The first thing to do when your capacitor blows out is to replace it with the right one. The stock capacitor is rated at 16 micro farads and 240V. Due to the way the motors are wired, the capacitor sees double the applied voltage, so under normal conditions 120 volts applied to the motor will apply 240 volts to the capacitor. Now if you add any kind of power fluctuation like a small spike, the capacitor is overloaded and blows out. What you need is a capacitor that is 300V and about 16-20 microfarads. The extra voltage in the rating gives the pump the ability to absorb those voltage spikes that would burn out the capacitor in the stock pump. They can be purchased at an electrical supply house for about half the price of a new pump. Be sure to tell them you want an AC capacitor. A DC capacitor would quickly burn out without ever starting your motor.
While we upgrade the capacitor, lets also add a little safety feature. The simplest is a 6 to 10 amp slow blow fuse wired inline. If some trash gets in the pump that locks it up or the pump is started with a defective capacitor, it will quickly draw 12-13 amps. A 10 amp slow blow fuse will protect against a locked rotor, but will not protect against thermal overloading. In higher quality pumps thermal protection units come standard, but we need to add something for this pump. To provide true thermal protection we need to look at options including a thermal snap-disc or a manual motor starter.
The manual motor starter is the best way to make the HF and NT pumps safe as it has thermal overload protection built into it and can be used as an on off switch. The Allen Bradley part number is 600-TAX4 and you will need a heater, part no P32, rated for 7.7 amps. These cost $30-$60 and are available at your local electrical supply house. They may not have the Allen Bradley items, but they will be able to use the Allen Bradley part numbers to cross reference to whatever brand they stock.
Whenever you see a picture of a Harbor Freight pump on a processor, you will almost always see a drip pan. They leak from several places. If you ever run them dry without oil in them, you will damage the seals and they will leak past the seal. You will notice the drip seems to be coming from between the pump and the motor. I don't know of any fix or replacement seals so once it leaks there it will always leak there. They also leak past the threads on the in and out ports.
The input port has straight cut over sized threads. When you tighten a 1" pipe in it, only a single thread is catching and tightening. After you run the pump a few times, the vibrations will loosen it up and it will leak. People have used lots of teflon tape, to seal it. Many have become frustrated with how it will loosen up and start leaking periodically and have resorted to JB Weld. Once you go there the pipe becomes part of the thread. I've heard of all kinds of fixes for this leak. JB Weld seems to be the most successful long term. Note that while the NT pump also has straight threads here, they are not oversized and people don't seem to have the leaking problem we have with the HF pump.
The output port is not deep enough or relieved at the bottom like it should be. It's like they cut off the end of the tap before cutting the threads. What happens is the first thread bottoms out in the bottom of the hole. Again we have the case where only one thread is holding the pipe in the port and after a few hours running starts leaking. We see this in the cutaway picture above of the blue pump and the black pipe. The best long term solution I've seen for this leak is to cut off the first three threads of the nipple you are screwing into the port. When you do that, the nipple is not long enough to bottom out and then will tighten up across all the threads at one time like it should. Note the NT pump has a proper relief at the bottom of the threads and will usually tighten without leaking.
The priming port is a screw on the top of the pump. beneath it is a rubber gasket of some sort that biodiesel/ methanol / wvo will melt. When it starts leaking, remove the goo that used to be the gasket and wrap the plug with teflon tape before tightening back in place. The NT pump uses a nitrile gasket that holds up much better.
One other mention about the HF pump. The fan shroud on the back of the motor can become misaligned during shipping and crush up against the fan. If it is, the motor will not work. The fan shroud should not be touching the fan, and the fan should be able to turn freely. The latest HF pumps dont seem to have as much trouble with this as they did in the past. The NT pump has the fan shroud bolted in place, so it's not an issue with it.
Pumping Methanol and Mixing Methoxide
My personal preference in pump design for pure methanol and methanol containing lye is the double diaphram air operated pump with a bondable (groundable) housing and teflon diaphram. Here is an Example of an expensive one.