DIY Watermaker

[beau]

Most pressure washers quote maximum pressure available and total volume but not together. So it is a bit of a guess at what volume you will get at 700-800 psi.(pressure charts are difficult to get hold of, we are talking Ebay here)
For example one is rated at 2600 psi and volume is 5.5 litres a min, but that does not mean you will get 5.5 litres/min at 2600 psi.
Power rating is 1600 watts and I would imagine that you would start the unit with little or no pressure so start up current should not be a problem. The pump itself is made from Brass.
I have heard on this forum some time ago that these units were being used.

[s/v Jedi]

Pressure is too high and flow rate too low. But yes, it might work on a single small membrane.

If they don't supply pressure plus volume specs, the whole brand is suspect already. Here are the specs for Karchers: Kärcher Residential - Electric and Gas Pressure Washer Models - Consumer, Prosumer, Professional

All residential electric ones are too small. With the gas powered versions we can find something suitable even though they are capable of way too much pressure.

cheers,
Nick.

[thatboatguy]

I *think* that with a plunger type pump, your pressure and volume are going to be pegged to RPM. Reducing RPM should reduce both pressure and volume although it might not be linear.

Brass is not a suitable pump material for saltwater (my opinion).

George

[Cap]

JusDreaming,

Could you send me a copy of your watermaker plans. I tried to open it, but couldn't.
jae5_9@yahoo.com

Thanks...Jeff

[Brent Swain]

Friends have used the ceramic plunger 3GPM brass pressure washer pumps with a 540 gpd membranes for years ,with no problems.
It's always entertaining when someone announces "That which has worked well for years, won't work."
Brent

[thatboatguy]

It's always entertaining when someone twists one's words into ones one didn't speak. heh heh

George

[Tellie]

Following Brents posts over the past few years, I'm sure that's not what Brent intended. But he makes a good point on brass pumps. A point on which I agree. When considering the longevity, suitability and costs comparisons of the SS pumps and brass pumps on home built watermakers. The brass pumps easily win.

[akio.kanemoto]

Just out of curiosity, are we talking brass pumps on washers etc - or "proper" brass pumps from Cat Pumps etc? If washers etc - if anybody could point me to a washer that can be pieced and used for cheaper than buying a pump from Cat etc - I'd be very interested in hearing - as even the brass pumps (as opposed to SS) from Cat in Australia are hideously expensive.

Originally Posted by Tellie

Following Brents posts over the past few years, I'm sure that's not what Brent intended. But he makes a good point on brass pumps. A point on which I agree. When considering the longevity, suitability and costs comparisons of the SS pumps and brass pumps on home built watermakers. The brass pumps easily win.

[thatboatguy]

Originally Posted by Tellie

When considering the longevity, suitability and costs comparisons of the SS pumps and brass pumps on home built watermakers. The brass pumps easily win.

I agree, because you have not specified a particular pump and you have left out the word "reliability" in your list of characteristics. Frankly there are various qualities of brass out there just as there are any other metal. For a time, the market was loaded with some of the crappiest brass fittings I've ever seen coming out of Thailand for instance. Also, sometimes people mistake brass and bronze which are two similar but different alloys. And finally, my own little bomb shell, I don't think that stainless steel is a good choice for watermaker pumps either! But I'm careful to word things as opinion when they are opinion and as fact when they are fact.

So in the example of a 3gpm pump (so long as it's delivering that flow rate at ~800 psi head pressure) and a ~500gpd membrane actually sounds about right. And if it were lightly used and properly maintained it *might* last for years. Anyway I'd love to know the model number of that pump as well.

Finally, I hope my comment above reads as tongue in cheek. I tried to add a little chuckle and wink to indicate that I was not offended and not trying to be offensive. I have a set of opinions about how to go about doing boat maintenance that are based on my experience, obviously this is a process that is ongoing and I keep an open mind.

George

[Tellie]

You are right I did not specify a particular type or model of pump. Off the top of my head I don't know the model numbers but they are easily found on the web sites of the various manufacturers. There will be different pumps for different watermaker applications, so one pump won't always be the right one even in brass. I prefer Cat pumps but I feel General and Giant pumps will perform as well. There is not a whole lot of data to fall back on when using brass pumps with home made watermakers as most people assume right out of the gate that they must have a CAT SS pump or their system will fail in short order. I will hunt down the pump model number on the last one I have to give you a better idea. But just a quick glance at the costs differences, a SS Cat pump can be around 1K depending on where you buy it. A brass pump can be had for around $300. A repair kit for a SS pump can cost around $400 as well. You can buy almost five brass pumps for that price. While a SS pump will last a bit longer than a brass pump in normal use the numbers are clear. It's a lot easier and cheaper to bolt in a new brass pump than fixing a SS one. Just my thoughts and opinions garnered from my personal experience.

[thatboatguy]

I really like the Giant Pumps. I've had great luck with them so far.

George

[svcattales]

Originally Posted by Bradley

Does anyone know of good plans for building a 12 volt watermaker?

This is an update of my previous posts on DIY watermaker with pics of installation.

I built a 12 Volt watermaker from plans I bought on Ebay. My unit is driven by a 1/3HP DC motor and it is directly coupled to the high pressure pump. Designed output is 6.5 gal/hr with a power draw of 27 amps. With a bigger motor (1/2 HP) and different pump configuration you can get 8.6 gal/hr at 39 amps. I decided to go with the smaller capacity since it meets our consumption needs for running the system at least once/week. Also, I can support the lower power draw with solar and wind power without running diesel.

My system is complete except I haven't installed the membrane in the pressure vessel yet since I won't be using the system until I start cruising again in December. I did check out the pump/motor and pressurized system to working pressure of 800 psi. I can't comment on performance until I start cruising with it.

The plans were pretty good and there was a complete parts list along with web addresses and prices for all major components. The designer advertises a complete cost of $1,675, but I spent about $1,900 due to an upgrade and price increases on components. Despite having good plans, construction was a time consuming project and required lots of hunting for various plumbing connections, hoses, two-way valves, high pressure hose etc. This was more than a weekend project so if you don't have time to devote to it, you may be better off buying an off-the-shelf unit. The big pluses for me were a total custom installation that used up very little of my storage space and low intitial cost. The other benefit is the availability of all compontents/spare parts without the high cost of single source parts.

The designer was Bob Benglar and his email is benglar at tampabay dot rr dot com.

Pics of my installation:

[thatboatguy]

Looks like a nice clean install. What feed pump did you use?

George

[svcattales]

Originally Posted by thatboatguy

Looks like a nice clean install. What feed pump did you use?

George

George, The high pressure pump is called a Hydra Cell F20E. The pump can be ordered with numerous options for pump head, valves, flow rate, etc.

[anjou]

ive just spent over 1 hour reading all the pages and posts, .........I have to say, im still no wiser. Whilst i realy appreciate everyones shared input and experience, I cant see the woods for the trees and a lot of advice often clouds the issue with so many variations.

Im intending to make a machine which will run directly off the gen engine shaft via a pulley. The gen is run @ 2 hours per day at sea to charge batteries and provide 240 ac for other uses (sounds extravagant i know but as yet, im not responsible for that) So with the gen running anyway, it makes sense to use the engine to directly power the water maker pump. Direct useage of engine power is most efficient and wont contribute to damaging batteries with high loads. The genset and main engine are side by side and i hope to make it possible to use either engine in the event of one breaking down on a long passage

During the 2 hour run time, i want to make @ 40 uk galls/ 200 lts. Cant see much point making more just to waste it. maybe the genset run time can be cut to 1 hour, in which case, the watermaker production must be doubled to make same volume in half the time and thus save diesel/wear.

From the DIY point of view, the 2 most expensive items are the membranes and pump. Im still unclear about the pump choice. Obviously a high pressure one with enough capacity to provide adequate GPH to make product and flush, but it has to be a piston type as no other will provide the 800 psi needed.

SS or bronze? It seems there is a split in opinion. Bronze is a cheaper, more commonly available type found in commercial machines, whilst SS is a bit more specialist and therefore more expensive. Am i correct in assuming the pump is like an engine with 3 cylinders in a block?
In which case, the block material is irrelevant, so SS liners can be installed with SS pistons?
Am i over complicating things?

Plumbing valves, pressure guages,fittings, hoses, prefilters, (dairy industry is a good source for housings and filters) etc are all readily available.

That only leaves the membrane. Not something which can be home made and has to be bought in.

It seems like there is more of a supply industry set up in the US for membranes. What are the options. Can they be bought direct from manufacturer or does it have to be through an agent? The pressure vessel (tube) has to be matched to the specific membrane i guess?

I dont normaly drink coffee but now seems like a good time.