Hydrodynamic (water pressure) question

I need a high pressure water hose, to remove sand building up and killing a tree on my lot. I don’t feel like renting the rig, so I thought about running two or 3 garden hoses together with y connectors, to give me a higher pressure, higher volume hose. The individual hoses come off of separate water pumps, so I should not be reducing the pressure by having them run at the same time. Will this scheme work? Will I get a higher pressure water stream out of the hose at the end? I tried to rig up a model at work using syringes, stopcocks and IV tubing, but my data was inconclusive (and I got glucose water all over me).

If they really are seperate it should give you some added pressure.

You’ll increase pressure by trying to emit the same amount of water from a smaller opening, hence the old trick where you put your thumb over the hose’s nozzle to quit it far.

What little I ever knew about hydrodynamics, I have long forgotten, so I’ll leave the science part to the others. I’ve gotten good results though with using those venturi nozzles. I would think though that in your case, it might be better to just run the three lines separate, tying them together at the nozzles, rather than running all three to a common nozzle?

Don’t confuse pressure with volume. Pressure is a measure of force per unit area, while volume is quantitative and measured in units/time.

It sounds like you’re trying to blast, so what you want there is high pressure and high velocity rather than high volume. Multiple hoses will not increase the pressure-- That’s determined by the pump(s). They will give you more volume though.

One hose, a high pressure pump and a good nozzle is what you need.

I left friction loss out of the picture for sake of simplicity.

thanks for the input.

From experience, I’d rather have higher volume than higher pressure, it moves more sand faster, and the water doesn’t soak away as fast. Perhaps it would just be best to tie 2 or 3 hose heads together, and increase the volume that way. Otherwise I think I would have to get a sand point attached to a high volume pump, and draw it up out of the lake.

also depending on the situation, you might be able to just leave water running unintended, even with low pressure and let the water flow carry the sand away.

Well, just look at this way. Suppose you din’t connect them, but simply aimed them at the same point. Pressure is force per area, and forces add, so the pressures would add.

tried that. Without a guiding hand, it doesn’t accomplish much. I’ve got to move sand from an area of over 100 square feet.

100 square feet? Have you considered a shovel, or maybe a push broom?

Let me restate that. I have to move over 600 cubic feet of sand. It’s an area at least 10x10x6 feet, and that’s just to best rescue the main tree. If I want to take care of the rest of it, I’m sure I’m dealing with over 1500 cubic feet. Having shoveled tons of sand in the past, I can tell you it gets tiring.

what is causing the sand buildup. Maybe you can make a wall or something to prevent it in the future.

The lake ate the original dune in 1986, when it hit an all time high water level, then ate it again in 1996, when it came up high again. Took out the dune, and nearly all of the stabilizing dune grass in our area. I’ve been cultivating the dune grass all over to get it growing again, and stabilize the new dunes, but in one problem area, the dune built up a lot faster and higher than the grass could grow in, right on top of a hundred year old black walnut tree. It’s healthy so far, but the tree surgeon says for long term survival, the load needs to be reduced on the roots.

I can’t just dig it away from the base of the tree, this would leave a crater which would fill right in again. I’ve sculpted dunes with water and dune grass before, so I know I can get this one to shift in a different direction and get it stabilized if I have enough water volume and pressure. of the two, I think volume is more important, otherwise the water is absorbed by the sand quite quickly. High volume water also allows me to shift a lot of the sand without completely trashing the stabilizing vegetation.

Probably a lot more than you wanted to know about this.

Oh yeah, I use snow fence in my efforts too.

Not quite. If you take three hoses and gang them together into a single hose (assuming all hoses are the same size and ignoring friction) you’ll get three times the velocity out of the final hose. The pressure needed to stop the flow, however, is no different. The forces add, but the areas also add, resulting in the same pressure. In your situation above, you also have three times the flow, but at the same pressure.

The trick is that if you are moving 1 unit/second of water through each of the three hoses, and it makes the transition through Y connectors to the single output hose, you’re now moving 3 units/second of water out the nozzle. No pressure difference is necessary to give a higher flow rate. (IIRC, the pressure will actually be lower in the output hose as the velocity increases - perhaps it’s been too long for me, though.)

Shiva’s post was more or less correct, I would just add that I think he missed the y-connector part of the OP, which would result in higher nozzle velocity. The same can be done with any kind of narrow nozzle, though, it’s just a matter of boosting volume to reduce the time spent hosing.

Good luck…