Archive for June, 2010

There’s a common misconception that a pressure washer can be used as a misting pump to run a misting system. It seems to make sense, since even a bottom-of-the-line pressure washer puts out plenty of pressure.

But you can’t use a pressure washer to do a misting job. The pressure washer is designed to spray at its rated flow rate for a limited time. There are no provisions for a pressure washer to bypass any of its water. Pressure washers use an unloader valve, which redirects the water to the inlet side of the pump. The water can be continuously cycled through the pump this way, but it will eventually heat up to dangerous levels, causing pump failure.

Misting pumps run usually at about 1750 rpm’s, that’s usually half the speed of a pressure washer. The misting pump uses a bypass regulator to keep roughly the same pressure on the mistline at all times. To do that, the pump needs to be sized appropriately to the misting system. You only need about 700 psi to get great mist, any more than that, the droplet size doesn’t change, you just push more water.

The key to long life of any mist pump is running it below its rated capacity by 10% to 20%. Having too large a pump requires too much water to be bypassed and then the pump gets hot and fails.

So, figure out your needs. You don’t need 1300 psi – you’ll break something. Be realistic and get a quality mister pump. Make sure it has a good water supply and it will last a long time. Fifty percent of pump failures are from lack of water or too much in bypass.