All inside tubes, inlets on the pump, and suction tube from fresh tank are 1/2". 3GPM pump, 40 PSI on the push side, self-priming up to 10ft (I think).Now, imagine fresh tank 6ft away, sitting on the ground on seasonal camp (no city water there). If I run 3/4" suction pipe to the pump, leaving the output side unchanged 1/2" - will it be better, worse, or the same? Plumbing theory suggests suction/input 1 size bigger than output, but I have a feeling that it will not matter much on this short distance. There is 0.5 micron sediment filter before the pump, with 3/4" outlets and 1/2" adapters, so I can have input tube either 1/2 or 3/4. Filters have been known to prefer larger input, too.

Better or worse what? Pressure? Flow rate? The answer to both though, is "No." The limitation is the inlet bore on the pump as well as the internal pump "plumbing" where the water passes through the diaphragm ports and check valves. The only practical cure for that is a pump with a higher pressure/flow rate capacity.

I had a 5.7 GPM 65 psi pump that drew from a 1/2" line in my last TT. It worked great and could provide flow to more than one faucet at a time. So I honesly dont think a bigger line would help especially with a smaller pump

No change.......Pump inlet/outlet still 1/2"Pump 3 gpm/45 psi regardless

"Better" - I meant easier on pump or better for a filter? Or - less cr-ap deposited in the tube before it gets to the filter (not really "less" cr-ap, but less notable in larger tube).

In theory the larger pipe would have very very slightly less internal resistance to flowing water.In practice it makes not one bit of difference given the low flow rate and fairly short distance you're dealing with. Reducing the suction head would likely have a greater benefit (if that is possible).A larger filter may possibly be of some value in terms of frequency of servicing it and its tendency to choke off the flow of water. That's hard to say without investigating the specifics of your setup and water clarity and so forth. Even with that, I doubt I know enough myself to make any useful recommendations.

Larger suction pipe to pump - better? | Good Sam Community

Dutch_12078
Explorer II
Oct 08, 2017
Better or worse what? Pressure? Flow rate? The answer to both though, is "No." The limitation is the inlet bore on the pump as well as the internal pump "plumbing" where the water passes through the diaphragm ports and check valves. The only practical cure for that is a pump with a higher pressure/flow rate capacity.
ScottG
Nomad
Oct 08, 2017
I had a 5.7 GPM 65 psi pump that drew from a 1/2" line in my last TT. It worked great and could provide flow to more than one faucet at a time.
So I honesly dont think a bigger line would help especially with a smaller pump
Old-Biscuit
Explorer III
Oct 08, 2017
No change.......

Pump inlet/outlet still 1/2"
Pump 3 gpm/45 psi regardless
Almot
Explorer III
Oct 08, 2017
"Better" - I meant easier on pump or better for a filter? Or - less cr-ap deposited in the tube before it gets to the filter (not really "less" cr-ap, but less notable in larger tube).
DrewE
Explorer II
Oct 09, 2017
In theory the larger pipe would have very very slightly less internal resistance to flowing water.

In practice it makes not one bit of difference given the low flow rate and fairly short distance you're dealing with. Reducing the suction head would likely have a greater benefit (if that is possible).

A larger filter may possibly be of some value in terms of frequency of servicing it and its tendency to choke off the flow of water. That's hard to say without investigating the specifics of your setup and water clarity and so forth. Even with that, I doubt I know enough myself to make any useful recommendations.
STBRetired
Explorer
Oct 09, 2017
X2 ^^^^
GordonThree
Explorer
Oct 09, 2017
When I plumbed my aux water tank to a 4.5 gpm 65 psi marine pump, I originally used a 1/2" right angle hose bib. It didn't supply enough water to the pump and there was considerable cavitation on the impeller. I upgraded to a straight 3/4" boiler drain valve and that solved the issue and improved the discharge.
joshuajim
Explorer II
Oct 09, 2017
GordonThree wrote:
When I plumbed my aux water tank to a 4.5 gpm 65 psi marine pump, I originally used a 1/2" right angle hose bib. It didn't supply enough water to the pump and there was considerable cavitation on the impeller. I upgraded to a straight 3/4" boiler drain valve and that solved the issue and improved the discharge.

A budget hose Bibb might have had an orafice of 1/4”. A full bore ball valve would have been a better choice.
westend
Explorer
Oct 09, 2017
No, it won't change delivery rate on the pump output. If you have a loss of pressure, elevate the aux. storage tank. The small diaphragm pumps used in most RV's do not have a big pump head lift. You could also put a bigger pump on the aux tank and use that through the utility fitting input.
Almot
Explorer III
Oct 09, 2017
westend wrote:
If you have a loss of pressure, elevate the aux. storage tank. The small diaphragm pumps used in most RV's do not have a big pump head lift.

I didn't notice a loss of pressure with 1/2 tube on aux tank. Little ugly noise-maker is pushing same sub-par flow (compared to average shore home) with same disgusting noise as it was with the built-in RV tank :).

The aux tank is sitting on the ground, its bottom is ~1ft lower than the trailer tank, but it's taller, so half the time the water level is at least same high as it would be in RV tank.