Homestead mailing list

[Bill Jones <billj AT harborside.com>]

Don Bowen wrote:

> I know Gene is looking into Ram pumps and I think several others may be 
> interested.  Today I looked at some home made ram pumps, made from plumbing 
> parts.  These would be good to experiment with.  The name is:
> Erosion Free Water Rams
> Don Price
> 563-519-0248
>
> He said that a ram needs a minimum of three feet of fall.  Lift water is 
> proportional to fall.  For 10 feet of fall, if lift is 50 feet, the output 
> will be 1/5 the input water, for 100 feet the output water will be 1/10 the 
> input water.  Five feet of fall will be half that and three feet will be 
> one third, 20 feet of fall will be double and so on.
>
>
>  
Our little seasonal creek dried up early and totally after the logging 
on the hill.  So I've given up on a ram pump for watering the summer 
garden.  But after thinking a while, I decided that it's still 
worthwhile to have one just for winter use.  If we had to use much of 
the meager winter output from solar panels on raising water from our 
deep well, there would be none left for lighting.  And why, with so much 
water on the surface (in winter)?

It's easy to show that this rule is true from the law of conservation of 
energy.  Since power is proportional to both height and the rate of 
water flow, and the power out will always be less than or equal to the 
power in, if the height doubles the the flow rate must be at least 
halved, etc.  But as I recall they were using an efficiency factor of 
about 60% at the webpages I visited, so expect the actual flow to be 
much less.

I found a source for PVC ram pumps ready-made for $150.  They have a 
clear window chamber and a diaphragm to prevent waterlogging (i. e., the 
cushiony air bubble in the chamber disappears and all the pressure from 
the ram is placed upon your plumbing system, possibly rupturing it).

By the way, another little engineering problem I've encountered is that 
I did not know how to predict the rate of flow through a tube exiting a 
holding tank (in practice this must be less than the flow rate at the 
source, otherwise the holding tank would eventually empty and air would 
be sucked down).  The key is to realize that the water will accelerate 
until the force of gravity on it equals the frictional force of the 
water line.  In other words, it accelerates until head loss equals the 
amount of head your have.  So if you look up the vertical distance the 
water drops in the _body_ of the head loss table, in the column that 
corresponds to your pipe diameter, then the flow rate off to the side 
will be the resulting flow!  You may have to estimate a value in between 
two numbers.

The reason for worrying about this is that the holding tank has to be 
deep enough to provide enough pressure so that even after the friction 
with the downpipe is overcome, there is still the minimum water flow to 
operate the pump (2 GPM in the case of the $150 model I found).  If the 
downpipe is fairly short, this is not a problem, but downpipes longer 
than 100' may require a fairly deep (more than a foot) holding tank to 
keep up the necessary pressure to sustain the minimum flow rate.  It's 
still not a problem, but for instance, a holding tank only 6" deep will 
not feed a terribly long downpipe properly, and it would be a nuisance 
to find this out after the fact, especially if the holding tank is 
placed inconveniently on a cliff side.

Bill
S. Oregon coast