RM Online - Know your nozzles!

A pump producing a certain volume of flow, perhaps five gallons of water per minute, is being forced through a nozzle with a very specific hole diameter. This nozzle restriction causes a pressure buildup that is uniform throughout the entire system, nozzle, wand, hose and pump head. The larger the hole, the lower the pressure.

Spray angle does not affect pressure. Yes, a 0-degree nozzle will shoot water and concentrate the stream farther than a 40-degree nozzle that defuses the energy of the water stream over the 40-degree pattern. But at the very tip it is at system pressure; in the wand gun hose and at the pump head, this is important, because if you over-pressure the system you may blow a hose or warp the pump head. (Always measure pressure at the pump - you lose up to 50 psi for every 100 feet of hose.)

When an unloader is adjusted to a certain pressure such as 1,000, 2,000 or 3,000, it will allow only the water volume through the nozzle needed to create the adjusted pressure. Any extra volume the pump is producing will be returned to the pump inlet through the unloader bypass.

When the trigger gun is closed, the pump is still producing water flow and all the pump flow is returned to the inlet at a returned "unloaded" pressure of 0 or near-0 psi. If the pump is left in this condition for five to seven minutes, the pump fluid will build up heat from friction through the valves, which could damage your pump un-less you have a thermo pump saver.

Nozzle size is very important. If you use too large a nozzle or a badly worn nozzle, all the water will go to the nozzle and you will not have enough left for your pressure requirements. Too small a nozzle will achieve your desired pressure but rob much of the cleaning power from your machine, because much of the water will be returned to the inlet.

When a piece of foreign material clogs the nozzle, it may stop the flow entirely, or just partially. If it is only partly plugged, it will act like a smaller nozzle and the washer will not feel as powerful as it should. In addition, with certain types of unloaders, if the tip is clogged, or if too small a nozzle is used, the unloader will cycle on and off.

Washers are measured in units of cleaning energy (uce): uce = gpm x psi. For example, 5 gpm x 3000 psi = 15,000 uce.

This is very important: when you pull the trigger gun, what you are mostly feeling pushing against your arm is flow (gpm), not pressure (psi).

So if you steal water from the nozzle, the washer does not feel as powerful as it should and does not have as much cleaning power and effectiveness as it could.

There are new color-coded nozzles indicating spray angles - red for a 0-degree nozzle, yellow for 15-degree, green for 25-degree and white for 4-degree.

You must also know your orifice size - otherwise you will reduce the effectiveness of the washer. Most washers indicate the correct nozzle size on the serial number tag. We constantly hear "The pump is bad" or "It needs seals because it has low pressure." Half the time we restore the pump pressure with a simple nozzle change.

All nozzles have a simple coded numbering system usually found on the nozzle face or on the nozzle side. A code of 25055 means this nozzle has a 25-degree spray pattern and an orifice of 5.5. A 15045 is 15-degree pattern and a 4.5 orifice. (Codes put the spray pattern, then orifice size.)

Nozzles are usually hardened stainless steel, but they do wear, so it's best to replace nozzles every year.

On the chart below, find your desired pressure; look down to find the gpm your washer is producing; then across to find your nozzle size. Pick a nozzle one size smaller than the chart calls for, for two reasons:

1. As the nozzle wears, less water is bypassed through the unloader and more water goes to the nozzle to maintain your adjusted pressure. When the nozzle wears so much that all the bypassed water is being used, you will start to lose pressure.

2. A trickle of water will slightly open the unloader bypass, so when you close the trigger gun it does not momentarily shock the system with a pressure spike.

Note that if you are in an area that has low water pressure, you may wish to use a smaller nozzle. The smaller nozzle will produce the same pressure, so you won't starve the pump and won't lose pressure despite a lower volume of flow.