like the idea of using an old differential for a gear box. cheap, and close to the right ratio depending on the pump. definitely close to the right ratio using the belly pto shaft (3.90 or 4.10 to one rear ends are common) and would get me a shaft speed of up to 4100 rpms.
but, using the rear pto would require almost twice those ratios or a pump designed to spin more slowly.
looks like i need what is called in the industry a "medium duty" washer capable of putting out 2000-3900 psi and about 3-4 gpm. most of those pumps seem designed for gas engines that run around 3600 rpm with direct drive. more expensive ones have belt drive. not sure why that is??
sounds like most of the money is going to be tied up in a good pump with good unloading valve.
here's the info i found on one site. didn't check their math.
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The type of cleaning that needs to be performed will determine the style of machine that will be necessary to perform the cleaning job. The amount of cleaning to be done will help determine the overall size of the unit. After determining the type and size of the unit you need a few other factors need to be considered. Pressure washer units, are offered with different heating sources (or none at all), weights, sizes, and overall construction.
Type of cleaning:
Earth dirt, road dirt, mud, etc. - Cold pressure washers are at their best when used on earth dirt, road dirt, mud, etc... generally where grease and oil are not a factor. A cold pressure washer with the help of a soap will be able to wash construction vehicles, clean sidewalks, parking lots, swimming pools, and cleaning jobs of this type and nature. Cold pressure washers are not the ideal choice for washing grease or grime (Grime is when you have dirt that is clinging to or ingrained in a surface). A cold pressure washer may move the grease and grime around but it will not clean the surface as it should, without the use of a very aggressive cleaning chemical. Cleaning a fifth wheel on a tractor-trailer would be a good example, the heavy grease is more likely to splatter and smear than to come clean.
Medium oil, gum, grease, and grime - Hot pressure washers are best suited for cleaning large areas quickly and where the type of cleaning is typically light to medium oil, gum, grease, and grime. The heated water in a hot pressure washer aids in the loosening of the dirt, and when soap is added, the dirt will come free of the surface. These machines will clean heavy grease deposits and grime, but will leave a slight grease or oil residue. A good hot pressure washer application would be a tractor-trailer. There are large areas that need to be cleaned, but the dirt is not caked on or very thick.
Grease, oil, animal, vegetable, or, mineral, contaminates - Steam cleaners perform best when used on grease, oil, animal, vegetable, or mineral, contaminates. T his is not to say that steamers will not clean other contaminates and surfaces. Steam will clean more thoroughly than a hot pressure washer, but will take longer on large areas. Steam cleaners have the capabilities of emulsifying an oil based grease or grime using the 325ｰF temperature. With the aid of soap chemicals (remember that soaps get more aggressive as temperatures increase) the job becomes faster and easier. Because of the high temperature it will also melt down such substances as honey, tar, most glues, etc... Steam cleaners also have excellent sanitizing capabilities because the ultra high temperature water will kill most germs, bacteria and viruses.
Continually changing applications - Combination units shine when the cleaning applications are continually changing and vary from one type of dirt to another. With a combination unit you have the best of all the other three units listed above in the same unit. So if you want to clean mud, leave the unit in cold-water mode, cleaning a truck, switch on the heat, and have a build up of grease and oil underneath the hood, switch the machine to steam.
NOTE: These are general guidelines presented to aid you in the selection of the pressure washer type that will work best for your needs. Please consult a professional pressure washer dealer to discuss what type of unit best suits your individual specifications. TOP of Page
Amount of Cleaning
After determining the overall type of machine (i.e. Cold Water, Hot Water, Steam Cleaner, Combination Unit) there are several other variables that determine the amount of cleaning a pressure washer unit can achieve. They are:
A. Pressure
B. Flow Rate (Volume)
C. Horsepower
The two most influential variables after the type of machine has been chosen are pressure and volume. These two factors will influence how quickly a cleaning job can be completed and how much the unit will cost.
Pressure, typically rated in PSI (Pounds per Square Inch), can seem to be the most impressive of the factors because of the large number associated with it. Pressure washers typically have pressure ranges from 750 to 5000 PSI, and that sounds really powerful. Understand, that the primary reason for the pressure is to help break the bond between the dirt and the surface being cleaned. Anything more than that is unnecessary and will just blow the dirt all over or cause damage to the surface being cleaned. Also, the higher pressure through the nozzle will cause the spray to atomize and become less effective for cleaning.
Volume, rated in GPM (Gallons Per Minute) on the other hand is what carries or flushes the dirt away. How fast dirt can be removed will be more influenced by the volume than by the pressure once the bond between the dirt and surface has been broken. Pressure washers appear to consume a lot of water, but this is not the case at all. The average pressure washer uses approximately three to four gallons of water per minute, whereas, the average garden hose puts out somewhere between six and eight gallons of water per minute. Using a pressure washer to clean is typically much faster and also helps save water.
The Horsepower of a unit will determine a number of different factors. The maximum pressure and volume, the voltage it can or cannot run on (i.e. 115V, 220V, etc...) and the amperage that it will draw. Typically the more horsepower a machine has will allow for higher pressures or volumes or a combination of both.
The pressure, volume, horsepower relationship holds true for cold and hot pressure washers, but not for steam cleaners. Steam cleaners typically are very low pressure and attain their cleaning power by using the vapor expansion of 325ｰF superheated water. Typically most steam cleaner horsepower ranges are from 1HP to 2HP. The unit's horsepower requirement will be determined directly by the volume and pressure.
The simplest formula is:
Electric Motor Horsepower = (PSI X GPM)/1460
Gasoline Engine Horsepower = 1.5 X (PSI X GPM)/1460 = 1.5 X Electric Brake HP
Note: This formula is the only true way to measure and compare different units i.e. two cold pressure washers or two hot pressure washers. However, it is not useful when comparing a cold pressure washer to a hot pressure washer or steam cleaner, since now there is the addition of a water heating system and in the case of a steam cleaner, the cleaning type is different.
A good example of the pressure volume relationship is to start with a 2HP motor. The motor is capable of producing 1400PSI at 2.1 GPM or 1000PSI at 3.0 GPM. With a standard pressure washer nozzle, the 3 GPM flow will have a greater surface impact than will the 2.1 GPM. The horsepower rating of the unit will be a limiting factor in the amount of work that a pressure washer can accomplish
