What is the correct pressure to pump to a TFT automatic nozzle?
Determine the correct pump pressure for TFT handlines by adding hose friction loss to the constant 100 PSI nozzle pressure. More pump pressure = more flow—no settings needed.
The pump pressure you choose is based on the size of the hose and what you want to flow. In the post that opened this thread, there is a comment about 100 PSI at the nozzle versus 200 PSI at the nozzle.
Not so! An automatic nozzle maintains a constant pressure at the nozzle.
Think of the nozzle as a screen door with a spring. If the wind is light the screen door does not blow open. As soon as there is enough wind to overcome the force of the spring on the door it starts to move and let some of the air go around the screen. The harder the wind blows the more the door opens but the FORCE against the door is constant as set by the spring.
The automatic nozzle is the same thing. It has a spring and it maintains a constant pressure if the wind blows harder (higher pump pressure) more wind goes through the door opening (around the door. If the pump pressure is INCREASED the nozzle opens up so that the increased FLOW uses more FRICTION in the hose to eat up the increased pressure. If the pump is 150 the nozzle will set itself to a flow that allows just enough water to flow to equal 50 PSI of friction loss so that 100 is left over at the nozzle.
If the pump is increased to 200 the nozzle will open more (the door swings) and it will let more water flow which increases the loss in the hose to where it equals 100 PSI. 100 at the nozzle plus 100 in loss equals 200 in that case. This is one of the neatest features of automatic nozzles, if the line needs more flow all you have to do is increase the pump pressure and you will get more flow and it happens without the operator having to set dials on the nozzle all he has to do is open the bail. There is a lot of information on this topic at the TFT website address www.tft.com.
The short answer to your question would be - Determine what flow you want to start with, figure the friction loss for the hose length that you use either by using charts or by experiment, add the pressure that you come up with to 100 PSI and that is the pump pressure.