Andy Pag attempts to rebuild a Spectra watermaker on a budget

Is a cheap Spectra watermaker worth rebuilding? Andy Pag shares a cautionary tale

Maybe I should have listened to the voice telling me to walk away, but I needed a watermaker after my Osmosea unit died and here was a Spectra unit, supposedly the Rolls Royce of watermakers, being advertised at a fair price.

Whenever the owner of something that’s not working tells you how easy it is to fix, ask yourself why they haven’t done so themselves.

It’d been left in a heap for a few months and who knows how many bits of it had stopped working in the meantime.

“You’ll probably find it just needs a bit of a clean” the seller chirped as I handed over the cash against my internal screams to turn and walk away.

A salinty metre on a watermaker for a boat

The Spectra salinity meter tells the control box when the product water isn’t clean enough for the tank, and the valve diverts it overboard. Credit: Andy Pag

The thing that sold it though was that I’d read Spectra sell a rebuild kit with all the internal parts that effectively make the unit like new.

Later that evening I learned these kits retail at over £1,000, for a handful of proprietary parts and a lot of imperial sized O-rings – not an option for me.

So the challenge began to see how cheaply I could get fresh water out of this thing.

The Spectra watermaker is essentially in four parts: the 12V pump, the pressure intensifier (also known as a Clark Pump), the membrane and the electronics.

A drill

Torquing bolts that go into engineering plastics has to be done very gently. Use the lowest clutch setting on your drill/driver. Credit: Andy Pag

Fresh water can permeate the membrane, which filters out salt, bacteria and most minerals dissolved in the sea water making it safe to drink, but it needs to be fed with a pressure of 60bar and a flow rate around 9lt/min in order to work.

The 12V pump is meaty, it draws up to 20A, but even that isn’t enough to get the pressure and flow needed. That’s the job of the intensifier.

It’s a collection of valves and pistons that cleverly recycle the pressure at the output of the membrane and add it to the pressure going in.

Over the first couple of minutes’ operation the pressure in the intensifier builds up and as it hits 60 bar the unit starts producing clean ‘product’ water.

Spectra watermaker: the pump

The 12V pump was working when removed but after 6 months in a cupboard, sorely needed restoring.

There’s a magnetic coupling between the motor and the pump head sealing the motor from any risk of leaks.

This is a unit that Procon made especially for Spectra. Spectra told me to ask Procon for spares and Procon told me to ask Spectra.

Osmosea watermaker in Andy Pag’s boat gave up the ghost and needed replacement. Credit: Andy Pag

Osmosea watermaker in Andy Pag’s boat gave up the ghost and needed replacement. Would refitting a Spectra watermaker be the answer? Credit: Andy Pag

The internals of the pump are an all-carbon vane pump. I found a rebuild kit for a compatible ‘Series 3’ pump for $70 from the US, but the shipping and import duty meant it would have been cheaper to buy one from Procon Ireland for €135.

Thankfully, in the bag of bits I’d bought was a spare pump head, and I was able to cannibalise both heads for enough parts to make one working one.

The vanes make a seal with the housing partly through centripetal force, and partly through a channel that sends pressure into the middle of the rotor pushing out the vanes. Once the channel was cleaned out the pump worked great.

■ Running total £0

Pressure accumulator

The pump is attached to a pressure accumulator to smooth the internal pressure.

This plays a key role, and without it, the pump’s magnetic drive can decouple during the pressure shock when the intensifier starts each cycle.

Mine had an internal puncture which I repaired with a bicycle tyre repair patch and pressurised to about 3bar with a bike pump.

■ Running total £1


The intensifier was the biggest challenge. It’s a 3D maze of seals and water channels, pistons and compression fittings.

Most of the parts that needed replacing were O-rings.

With a set of callipers I struggled to confidently size them, until it dawned on me that Spectra’s factory is in the US and everything on this machine was in imperial sizes.

eBay came to the rescue and the O-rings were cheap enough, around £20 for the ones sealing moving parts.

■ Running total £21

Removing the O-rings

To remove the four O-rings in the tight spool housing, Specta sell a special tool.

an oring of a Spectre watermaker

Removing the O-rings from the Spectra’s inner shaft takes some patience at first. Credit: Andy Pag

I used a dental pick which I fashioned into a spiral hook to do the job.

The first one took 40 minutes to remove, but then I had the technique down pat and the tool perfectly turned, and the last one came out in under a minute.

■ Cost of dental pick £3
■ Running total £21

Compression fittings

There are eight compression fittings on this unit. Spectra sell them for $130-$150 each. My heart sank.

Their NPT thread, unlike the common BSP thread makes them hard to find in the UK. And worse; it’s a parallel thread, which is even rarer.

I discovered that Spectra has these parts specially manufactured out of nickel bronze. This is a design choice I’m not happy with.

The material suffers from electrolysis as it connects to stainless steel pipework and the fittings dissolve over time.

The residue then permeates through the intensifier and wears away at the tight-fitting moving parts, reducing the intensifier’s ability to generate pressure until the unit slowly dies.

PTFE tape around a metal pole

Using PTFE tape in the compression fitting to slow electrolysis. Credit: Andy Pag

Spectra won’t change the fittings back to stainless. The reason, they told me, is because stainless fittings trap water between the thread and the plastic housing they screw into.

Over time that water putrefies and attacks the stainless. As it rusts, it expands and cracks the plastic housing leading to leaks.

They say that if the machine is flushed with fresh water after each use the corrosion is limited.

Other manufacturers, Schenker and Osmosea, haven’t reported this problem and happily use stainless compression fittings.

I wonder if a bit of liquid PTFE would solve the problem?

Smothering the threads of the compression fitting with Duralac in the hope that it will slow electrolysis. Credit: Andy Pag

Smothering the threads of the compression fitting with Duralac in the hope that it will slow electrolysis. Credit: Andy Pag

In the end I was able to find replacement fittings in stainless steel made by Swagelok sold as a job lot of 12 for £20, but after I bought them I decided not to use them as they had a tapered thread.

Screwing a tapered thread into the plastic housing can split it. It’s very hard to judge how much pressure to apply, and if you overdo it, the machine is a write-off.

Instead, I cleaned up the existing fittings, and used a combination of PTFE on the olive and Duralac on the thread to reduce the conduction between the two components.

In practice the best this might do is slow down the decay. My choice meant I’d have to flush the unit with fresh water after each use.

Spectra’s computer is programmed to do this so these components aren’t sitting in saltwater but it reduces the overall efficiency of the machine’s output as it uses up some of the water it’s just made.

■ Cost £20 – wasted
■ Running total £41

Annular rings

Inside the intensifier I could see thin pencil lines on both the annular rings.

I ground down a washer to mimic the special tool Spectra sell and used it with a punch to tap them out.

The pencil lines were actually cracks, probably caused by the nickel bronze debris, and leading to the failure in pressure which prompted the seller to give up on the machine.

A blue Dual TDS Meter

Dual TDS Meter shows how much saltwater goes into the Spectra watermaker and how much clean ‘product’ water comes out. Credit: Andy Pag

This is a bespoke part and I saw no option but to pony up the £80 each which Spectra dealers ask, but then I spoke with Jim Cudd at Sailfish Marine.

“I have an old bag of spares for that machine. I just have to find it,” he said.

Three days later he sent me a picture of a treasure-trove of parts. Some were used – too good to throw away, but not good enough to use on a client’s machine, some were new – unneeded spares from previous rebuilds, and some were ‘provenance-unknown’.

I replied listing the parts I needed and he responded by sending the whole bag free-of-charge.

In the envelope were five annular rings. One had ‘old’ written on it, but all five looked pristine. I picked the two closest matching, hammered them gently in, and sent Jim £20 for a few beers.

■ Running total £61

Continues below…


The main pistons and cylinders looked OK, but the check valves were seized with green verdigris, quite an achievement for plastic and rubber components.

The plastic bits cleaned up but the rubber was too brittle to make a good seal.

Thankfully Jim’s magic envelope contained four complete sets of valves. The unit went back together and I plumbed it to the pump and the membrane.

Measuring the purity of the output – not as clean as I’d hoped but OK for now. Credit: Andy Pag

Measuring the purity of the output – not as clean as I’d hoped but OK for now. Credit: Andy Pag

Ignoring the electronics, I wired 12V straight to the pump. The salty water circulated, flushing out the air and then the moment of truth, I closed the relief valve and ‘psstching’ the pressure intensifier pistons started reciprocating.

It took a few moments and water appeared from the output pipe. I timed it and it was flying out at 60 lt/hour, exactly on spec, but the water quality was 700ppm. 500ppm is the recommended maximum for safe drinking water.

Clearly the membrane was showing the signs of its neglect.

Spectra sell two sachets of cleaning solution, which are essentially an acid to dissolve limescale build up and an alkali to break down organic growth.

Assuming the blockage was organic growth I ran a homemade alkaline caustic soda solution through the machine.

■ Cost £3
■ Running total £64

Electrical connections

I also improved the electrical connections to the pump on my test bed.

Any resistance in connections can reduce the pump performance and have a marked impact on the water output.

This time the water quality was 550ppm. There’s a chance that with regular use this might improve over the next month, otherwise a new 40in membrane costs around £250 from Lenntech in The Netherlands.

A assembled Spectra watermaker

The reassembled Spectra watermaker ready to be installed below the sole. Credit: Andy Pag

Even though the electronics all seemed to be working I decided to bypass them and use the pump manually.

When the sensors fail, an installer told, me they aren’t economically viable to replace and he recommends owners go manual.

It takes about two minutes for the unit to get up to pressure, and the output is initially pretty grubby, so I connected a simple timer circuit to the diverter valve which directs product water away from the boat’s tank for the first three minutes after start up.

■ Cost £7


Even the Spectra dealers don’t want to work on these things, and I can empathise, as they suck hours of time without a guarantee of success.

Most of my time was spent learning as I went and if I were to do it all again it would take a tenth of the time.

Most Spectra parts have generic equivalents that can be sourced cheaply online.

Spectra’s choice of materials means the most likely fault with the machine will be annular rings being scratched or cracked by crud from the nickel-bronze fittings.

These are a proprietary part and have to be sourced from Spectra.

■ Grand Total £71… plus countless hours that could have been better spent!

Enjoyed reading Can I rebuild a Spectra watermaker?

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