SURFACE CLEANER GUIDELINES Use two bar surface cleaners. Three or four bars spreads your power too thin. I recommend using 15 degree nozzles for the 20-24" surface cleaners and up to 10gpm. 28-36" surface cleaners with 10+gpms use the 25 degree nozzles. Use the barens nozzle calculator to figure out the correct size nozzles to use for your machine. Divide gpms by two for two bar surface cleaners. 20" surface cleaner: 13-26hp 4-8gpm @ 4000-3000psi 24" surface cleaner: 18-33hp 5.5-10gpm @ 4000-3000psi 28" surface cleaner: 24-40hp 8-13gpm @ 4000-3000psi 36" surface cleaner: 33-53hp 12-17gpm @ 3500-3000psi http://www.barens.com/cgi-bin/calc I used this chart and also measured the area of a circle. From my experience this HP-GPM range for each setup (slow-fast) is pretty accurate. You will be able to move each one about the same speed for it's range. Area of circle = pi X radius squared. 20" = 314.159 inches squared 24" = 452.389 inches squared 28" = 615.752 inches squared 36" = 1017.875 inches squared Your HP & GPM should be directly proportional to the surface area your machine will cover. 28" circle is 2.00 times larger than 20" so you need 2.00 times the HP & GPMs. 36" circle is 3.25 times larger than 20" so you need 3.25 times the HP & GPMs. 36" circle is 2.25 times larger than 24" so you need 2.25 times the HP & GPMs. 36" circle is 1.65 times larger than 28" so you need 1.65 times the HP & GPMs. If you have more than one machine join them together to make more HP & GPMs. You'll need a high pressure T and a short whip line. Both your unloaders must be pressure actuated, and both pumps need to have the same pressure so they will be balanced and run at the same rpms. If your surface cleaner comes with a 1/4" hose from the gun to the swivel, take it off and replace it with a 3/8" hose. Also the guns on the surface cleaner will eventually wear out and break, and they also restrict your flow slightly. To avoid any problems, take it off and use a quick coupler attached 3/8" heavy duty zinc plated steel 3000psi ball valve. Example- 18hp 5.6gpm @ 3500psi + 13hp 4gpm @ 3500psi = 31hp 9.6gpm @ 3500psi 20hp 8gpm @ 2800psi + 13hp 5.5gpm @ 2500psi XX DOES NOT WORK! XX I tried this combination and it caused my smaller machine to cut off and stall from the pressure difference. If I ran the 5.5gpm pump with a 15-16hp engine this combination would work. 20hp 8gpm @2800psi + 13hp 5gpm @2800psi = 33hp 13gpm @2800psi WORKS! 20hp 8gpm @2800psi + 11hp 4gpm @3000psi = 31hp 12gpm @2900psi WORKS! VIDEO DEMONSTRATION of 13gpm @ 2800psi on a Maxima 36" concrete cleaner Using large intakes are especially helpful when running large volume 8+gpm machines. Use a 2" single union ball valve attached to your bulkhead, attach to a 1-1/2" filter, attach to 1" hoses to your machines. Keep your 1" hose short as possible for maximum flow intake.