Gravity Water Pressure

[CurlyDave]

if I plug the vent on the top of the holding tank installed 10 feet BELOW the top one. I thought it would kind of step up the pressure...

There are a couple of possibilities, none good.

If you actually plug the vent completely, it is certainly possible to pressurize the lower tank, which runs the risk of bursting it. It is only built to withstand unpressurized water inside it.

Even worse, if you withdraw water from the tank faster than the inlet can make it up, you will place the tank under vacuum and run the risk of collapsing it when you open a water faucet down below.

Holding tanks are designed for storage of water -- they are neither pressure nor vacuum vessels.

I propose that the reduction in pipe size as they neared the nozzle only reduced the effectiveness of the water cannon by creating more loss due to friction. It was likely cheaper to use smaller pipe and easier to move around. The nozzle itself is where the high flow/low velocity is switched to low flow/high velocity. Would have been great fun to run a cannon like that.

I think Highbeam is right on this. By tapering down the very tip of a pipe discharge velocity can be increased, but it is not done by slowly reducing pipe size in steps. For a given pressure and flow rate it is possible to calculate exactly the pipe shape which will produce the maximum discharge velocity of water. The reduction is not quite the shape most people think, and is surprisingly short. For a good example, examine a fire hose nozzle which is designed to produce the maximum water velocity and distance of travel.

The nozzle is typically only a few pipe diameters in length.

 

[bugstruck]

Adding water volume (second tank) below the first tank won't help with pressure. Vertical head is creating the pressure. Wouldn't matter if it were 5 gallons or 5,000. Now if you raise that spring.....or lower the cabin..... /forums/images/graemlins/tongue.gif that would work. So too would a booster pump. 250 gallons should easily serve 3-4 people for a day assuming it refills in 24 hours or less.

 

[johnk]

The tank will fill in about 4 hours as this is a pretty active spring.Where the spring comes out of the ground I built a cinder block barrier arounf the source with 1 1/2 PVC coming out of the side of the cinder blocks. I covered the top of the blocks with plexiglass. From here it goes roughly 60 ft downhill to the holding tank and then another 500 ft downhill with 1 1/4 well tubing to the cabin. When I leave the cabin in the winter I open the lower end of the tubing and let her run all winter. Never froze yet in the 7 years I,ve had it..The running water runs down to a culvert on the side of the road. Thanks for all the info....

John

 

[turnkey4099]

</font><font color="blue" class="small">( Would putting another holding tank just below the main one help or hinder the pressure or make no difference if I plug the vent on the top of the holding tank installed 10 feet BELOW the top one. I thought it would kind of step up the pressure... The more water in reserve the better. Thanks for all the replies.

John )</font>

Kinda hard to picture that. Plugging it will only increase pressure by the additional amount of head you will get in -that- tank. As someone else mentioned you then have the vacuum effect probem. In general you can't increase your pressure by playing with pipe sizes, tank sizes, etc. YOu might gain some by increasing delivery pipe size but as you are already running 1 1/2 any increase would be minimal.

If you need more pressure you can only gain it two ways.

1. Raise the elevation distance between tank and house
2. Install a pressure booster pump at the house or a pump at the tank feeding a pressure tank.

Harry K

 

[bugstruck]

John,

Sounds like a great setup to me. I have 35 to 50 PSI (pressure switch window) on a well pump and I can't shoot water 60' from my hose at 50 PSI. Maybe 40' on stream nozzle. I wouldn't change a thing. Per your comment, the winter run-thru seems to work great to mitigate freezing. Way better than many pump and pressure situtations for an over-winter, assuming the heat is off. How far are you from me? Maybe you could run a line over here.... /forums/images/graemlins/wink.gif /forums/images/graemlins/grin.gif

 

[1948berg]

Stupid question: How do they get water up to the top floors in skyscrapers, and how is it taken down again whitout getting 1000 feet of water pressure in the pipes?

 

[Highbeam]

PRV, pressure reducing valves kinda like a pressure regulator on a barbecue. You still need a mighty booster pump to get it up there though.

We even put them on the services to homes located at the bottom of huge hills if the potential pressure will be too high like 90 or more psi. A simple little device that is adjustable with a setscrew.

 

[gizmo]

If you have that kind of elevation change and are lucky enough to have reasonable flow rate, you might consider a generator. For example, a flow of 150 gal/min falling 60ft would easily produce 1000W, and ideally, almost 2000W. A 2” PVC line will handle that kind of flow.

 

[johnk]

Good thought, but the flow rate iwouldn't be enough to run a generator. There is enough water though for my needs. I like it because it isn't a very complicated setup and it works. No moving parts or power needed. Thanks for all the ideas and answers...

John

http://users.adelphia.net/~gizmo/

 

[Bird]

Even though Central Texas is fairly flat, our place in the country was about 2.5 miles downhill from the water company's water tank (not an elevated tank and I've forgotten exactly what the elevation drop was) but the only time I checked the pressure, it was over 80 psi, so I put one of those pressure regulators on the line going into the house with it set for about 50 psi.