loss of pressure

[Chappy 138]

I have a CAT 45G gear reduction pump on a 4/4000 machine with a pressure actuated unloader. The problem I have is when hooked to the tank, It takes 15 seconds to upwards of 60 seconds to build up pressure. I've made sure there are no air in the line and the line is 3/4". When hooked directly to the water source it does not do this. The dealer said it has to do with the temp sensor, that after it is idling for a while, the temp sensor bypasses the unloader to reduce temp. and when this happens it allows air in the unloader. (thats as close as I can remember to what he told me anyway.)

Obviously this is a pain in the butt, and on a 3 hour job yesterday that took a lot of hand scrubbing, I probably wasted 20-30 minutes. Not acceptable. what can I do to aleviate this delay in pressure build up? I dont have to use the tank most of the time, but there are some commercial jobs Im bidding on that will require it.

[Grant 500]

Is your tank above or equal in height compared to the pump? Sounds like there is not enough head pressure from your tank. Try a small 12 volt pump or raise the tank higher than the pump inlet.

[One Tough Pressure 580]

I agree with Grant. How long is this 3/4" hose that is connecting the unit and tank?

[Chappy 138]

the tank is above, the line is 6 feet

[One Tough Pressure 580]

I have seen units set up like that. Some worked some did not. Aside from the 3/4" hose, what else is in the plumbing mix? Misc fittings, filters (are they clean), ball valves and so on. You may want to try using 1" hose.

[RyanH 14]

I use a 3/4" hose with a reducing fitting to go from the 2" to the 3/4" opening. I have to have about a 1.5' head between the pump and water tank outlet before I get consistent flow. Otherwise, I get a lot of "knocking" from inconsistent flow. Mine is direct drive, if that helps. Fortunately, I rarely have to use my own tank. Tank has about a 2.5 - 3' head when full; as tank volume decreases effectiveness of pump pulling water decreases.

[Grant 500]

First are your hoses going directly to the pump and not a float tank? If so

Try changing the 3/4 hose to 1" or bigger schedule 80 PVC since you have a 2" opening in the tank anyway. Use maximum diameter as close to the pump as possible to increase available volume.

If you must use a hose, do not use a garden hose because it is designed for pressure not suction and will collapse very easily. Clear braided hose is okay but make sure the ID (inside diameter) is at least 3/4".

or since you dont use it much anyway, can you set up a 12volt booster pump so you have more pressure on your supply side?

Some folks will argue that direct drive pumps dont have the pull of a belt driven set up. I dont know for fact as I have only ever had belt drives.

[Chappy 138]

my pump is a gear reduction pump that should pull with no problem, I use braided line, with no valves or anything else in between pump and outlet.

Ill try the larger diamater line and shorten it to see if that works.

thanks for the replies.

[beyoungsr 14]

Jon,

I think the pump is loosing prime. Is the bypass routed to your tank? I would guess not. Doing this would reduce any chances of the pump over heating. A couple of ball valves and a tee would take care of this. This arrangement will bypass to the tank and allow the machine to run all day in bypass with no problems. When you are not using the tank close the valve going to it and the bypass will run to your filter or incoming supply.

Install a tee and ball valve in your supply line from the tank.

Fill the tank and before leaving your house and attach your h.p. line to your pump along with an open wand.

Screw on your garden hose and open the ball valve. Turn on the water and fill the line while watching for water to exit the gun. When water flows from the lance close the trigger than the ball valve.

You should be free of any air now. This can also be done on site.