A couple of thoughts, from a Factory Authorized Village Marine
Tec sales & service
Many watermakers have been home and factory built with the industrial CAT pumps, which can be purchased at a relatively reasonable price
(one source online is McMaster-Carr, a large industrial supply chain. McMaster-Carr
. The bronze head
pumps are almost a waste of money
, the SS heads are pretty hardy, and not really hard to rebuild
(either one). McMaster can also sell you the parts
, or a complete head
assembly. This is a big plus if you're cruising in US waters. A phone
call and a credit card should get you what you need in 2-3 days no matter where you are in the continental US.
The one thing I'd be wary of using a pressure washer pump is the possibility (probability) of small amounts of its crankcase oil
getting into the feedwater. If this is the case, you'll have steadily decreasing production, and the chemical cleaning
process will be of limited help. The cost savings in the pump will ultimately be consumed by the need to replace membranes. On top of that, these pumps are not at all designed for salt water
, and you'll probably replace it on a regular basis. Corrosion
by-products will be passed to your membranes and that won't be good. Much worse, they will get into your high pressure regulator
and that will be bad.
If you're designing your own system, one very important thing is insuring that there is enough discharge flow relative to the product output, about 10:1, as a rule of thumb. That means for every gallon of fresh water
that comes out, 10 gallons of seawater is dumped back overboard
, about 10% saltier than when it came in. This all has to be supplied by the HP pump. You can get about 7 gallons per hour of product for each 1 gallon per minute of pump capacity at operating pressure. The actual performance of the pump will be significantly different with the typical booster pump supply pressure of 10-15 psi, compared to the 40-50 psi from a household water
supply. Insufficient flow will give you problems with mineral scale buildup in the membranes. Again, the chemical cleaning
process won't keep up with it, and you'll be replacing membranes. If you buy a CAT pump, you can go by the manufacturer's specs, and their tech dept (if you don't find the info in the full specs) can tell you how much flow you'll get at a particular operating and feed pressure, and you can select your membranes accordingly. You cannot go by the specs that come with your pressure washer. They give you two totally separate ratings, max. pressure at 0 flow, and max flow at 0 pressure. You'll have to set it up and test, with the booster pump, HP regulator and a flowmeter, before you can determine the actual capacity and select an appropriate membrane.
OK, now I'll have to insert the 'plug' for what I sell. Village Marine
HP pumps have titanium
, and the head, called the 'manifold assembly' is warranteed for life
. If you take nominally good care of it, you will likely never see the day you replace or repair it.
On double duty as a pressure washer, you must keep the hose run very short, or you will have dissapointing results. I've seen it done.