I have a physics question.

[Montresor]

OK so I need to understand something.

We have a rain barrel with a spigot at the very bottom and it's got a few feet of hose.

1. What effect does gravity have on the pressure coming out of the hose?

2. If I lift the loose end of the hose higher than the water line will it cease to drain??

3. If there is ~500 pounds of water exerting pressure on the spigot, which is ~2 square inches, then we have >200 psi at the outlet ... but if I want to bring the water back uphill, how much pressure do I lose?

4. What, exactly, is the relationship between h (height) and p (pressure)? Do diameters come into effect?

I took fluid physics in University but man that was a long time ago, and I half-assed tried to search through Google but it didn't really work for me this time.

I should just summon @Duxwing lol. I need help buddy.

 

[Matt3737]

Are you looking for the wikipage on Siphoning? http://en.wikipedia.org/wiki/Siphon

I don't know if it has all the specifics to your questions though. I haven't read through it all yet.

 

[Montresor]

I'll read thru it again and see if it answers my questions. I'd feel pretty dumb if it did seeing as I've probably read it five times over the last five years.

 

[Architect]

OK so I need to understand something.

We have a rain barrel with a spigot at the very bottom and it's got a few feet of hose.

1. What effect does gravity have on the pressure coming out of the hose?

Only related to the height of the barrel, not the width. You can have a hose of the same height instead of a barrel and it would have the same pressure.

2. If I lift the loose end of the hose higher than the water line will it cease to drain??

Yes

3. If there is ~500 pounds of water exerting pressure on the spigot, which is ~2 square inches, then we have >200 psi at the outlet ...

See above

but if I want to bring the water back uphill, how much pressure do I lose?

It depends of course on just the differential distance

4. What, exactly, is the relationship between h (height) and p (pressure)?

I forget, a search should suffice

Do diameters come into effect?

Not unless you have a hydraulic system. A dam has just as much pressure if it's only holding back a foot of water, as long as it's the same depth.

 

[Montresor]

If you use the pics as a reference, I'm trying to use the water in the drum to fill the washing machine whenever beckoned.

Easy enough to keep the drum full.

 

[Montresor]

^oops I didn't see Architect's post yet.

okay so if I raise the drum up a few feet, then the pressure at the hose outlet would be equivalent to the pressure in the drum at the corresponding h??

The washing machine inlet is near the top. I think I'm looking for around 40 psi of static pressure at 3' of head.

 

[MissQuote]

If you are trying to use the water in the drum to fill the machine wouldn't the easiest solution be to just lift the drum up on a shelf that is only a foot or so below the top of the washer?

Would it sill collect the water the same if you did so? Because that would solve your gravity/pressure problems on a practical level.

 

[MissQuote]

Oh, I didn't see your last post before I posted.

Well, there you go.

 

[Duxwing]

EDIT: Defer to Architect's judgement, he's the one with all the physics know-how.

-Duxwing

 

[Matt3737]

As far as I'm aware, Montresor, your only concern should be having an airtight hose to maintain vacuum pressure to get the fluid to flow upwards. The spigot may or may not be airtight. I think placing the tube through the opening in the top into the water would work better, then apply some vacuum pressure and voila, siphoning!

 

[Montresor]

Matt3737 you are talking about something different. I do not wish to have a siphon in this system because it would either have to be primed every time I go to use it or I would have to install pumps and valves. Plus the potential for a flood vastly increases when a siphon is at work in any system.

What I want is static pressure at the hose outlet which is going to be 3' off the ground. It has to be as if the washing machine is connected normally.

Mounting evidence is leaning towards building a rack to lift the drum high up off the ground. Something I was hoping to avoid but am more than willing to do.

I have posted the same question on a different forum and I'm getting similar (plus conflicting!) answers, but what I share in common with those people is very different from what I share in common with you people .

 

[Montresor]

So this project has taken a turn for the more complicated, after discussing the particulars with a very reliable source.

The front-loading washing machine has diaphragm check valves at the inlet, which require a pressure of ~50 psi to overcome. To achieve this pressure with gravity alone, one would need a water tower (apparently.)
The electronic cycle will fail if the washer doesn't fill in time.

The next line of attack is to implement a buffer tank into the system which has been installed in such a way that it can be filled with a low pressure hose (from the water barrel), pressurize the water, and be available at the beckon call of the washing machine.

I know that this isn't much of a physics question anymore but has anybody done this in their house or job before?

 

[Architect]

So this project has taken a turn for the more complicated, after discussing the particulars with a very reliable source.

The front-loading washing machine has diaphragm check valves at the inlet, which require a pressure of ~50 psi to overcome. To achieve this pressure with gravity alone, one would need a water tower (apparently.)

Correct. This is how they get water pressure in high rise apartments, by putting a water tank on the roof, to which they pump water from street level. Long tradition and story of the wood water tank industry in NYC by the way.

To do what you want you'll need to pump water to the top of the house, and then have a return feed going into the washer. You don't even necessarily need a big tank which serves as a buffer. A fast pump and small tank can suffice, worst case a tank equal to the volume of the washer. Alternatively you can get a pressure tank at the same level (water is pumped into a tank at higher pressure), but that will cost more upfront and in electricity.

The final and simplest option is to keep the machine hooked up to the house system, and simply fill up the tank from the rain bucket using a siphon when you wash. The machine should sense that the tank is full or nearly so (maybe needs a top off) and off you go. I'm pretty sure washers sense full by sensors and not with an incoming counter, much more reliable that way.