Can I add a second Membrane to my Spectra Cape Horn Watermaker?

[andyalford]

I have a Spectra Watermaker - Cape Horn Extreme
It uses 2x Shurflo 12V pumps (8008-943-839) and can be operated with one or both pumps.

These are connected in parallel to pump 2.4 GPM (550 LPH) at 90psi (max ideal condition)
This feeds into the Clark Intensifier pump, which multiplies it into a single membrane.
In the real world, it produces 8% as product, that’s about 12 GPH (45 LPH)
The unit is 5 years old, and will run from Solar panels using 18A, so that’s pretty good.

The unit can be run with just one pump.
Inlet Flow falls from 550 LPH to 300 LPH
The inlet pressure drops from 90 psi to 70 psi
Product Flow falls from 45 LPH to 24 LPH
And quality rises from 320ppm to 370ppm, but current drain is halved at 9A

So that made me think that I could add a 2nd membrane in series with the existing and still run it with 2 pumps.
I have 2 spare pumps anyway, so I could try running with an optional third pump for “turbo” mode.
I would not expect to double output, but I would be operating lower down the “performance curve”

Anyone thought about this, or even tried it?

However, if I had 2 membranes would the system still function with only 1 pump?

(I am changing the membrane anyway, and giving the Clark Pump a full service, so I thought it was worth pondering…)

[clownfishsydney]

Pretty sure that two membranes will not make more water. As far as I can ascertain (we have a Spectra), the best thing is two pumps which doubles the output as you have stated.

[andyalford]

Originally Posted by yachtshah

So that made me think that I could add a 2nd membrane in series with the existing and still run it with 2 pumps.
I have 2 spare pumps anyway, so I could try running with an optional third pump for “turbo” mode.
I would not expect to double output, but I would be operating lower down the “performance curve”

I'm wondering if 2 membranes and 3 pumps might produce 150% output, perhaps more.
Given that 1 membrane + 1 pump produces more than 50% product, but slightly lower quality, and produces less wear on the pump head.

I believe the Clark pump is a generic item - the manifolds produces 8-10% product and the pump multiplies pressure from 80psi to 800psi using a valve on the manifold exhaust water. I see the same pump is in the Newport 700 & 1000 which have 2 & 3 membranes respectively.

[newhaul]

Shoot tellie a pm he is the resident spectra guru.
Cruisers & Sailing Forums - View Profile: Tellie

[Matt Johnson]

Originally Posted by yachtshah

I'm wondering if 2 membranes and 3 pumps might produce 150% output, perhaps more.
Given that 1 membrane + 1 pump produces more than 50% product, but slightly lower quality, and produces less wear on the pump head.

I believe the Clark pump is a generic item - the manifolds produces 8-10% product and the pump multiplies pressure from 80psi to 800psi using a valve on the manifold exhaust water. I see the same pump is in the Newport 700 & 1000 which have 2 & 3 membranes respectively.

Are they the same Clark pump? I thought they offered different pump efficiencies as an indicator of size of system..... like, the 12% was for the 200gpd and the 8% was the Clark in the 700gpd (just throwing those numbers out as I can't remember).

I know my HRO's "clark pump" is for the 200gpd and they have a different part number for the higher output units.

Matt

[andyalford]

Originally Posted by funjohnson

Are they the same Clark pump? I thought they offered different pump efficiencies as an indicator of size of system..... like, the 12% was for the 200gpd and the 8% was the Clark in the 700gpd

Good observation, and I agree.

The pumps are different for different recovery rates, but I would aim to keep that the same at about 7-8%. It would be the flow rate that would increase.

Having said that, it seems another membrane casing and plumbing would be close to $1000, so my enthusiasm for this project is waning really fast!

[Kenomac]

Then short answer is: No.

[Larry Florida]

The long answer is maybe yes. The second cartridge will be less efficient than the first as it sees higher retentate concentration (higher salt), less pressure and less flow. For sure it will put out more than one cartridge in all cases, i.e. the second cartridge will produce some output.

[Kenomac]

'Seems that after receiving your very nasty PM that you only want yes for an answer.

Then go for it! Please get back to us on how it works out after you spend the $1000.

[newhaul]

Originally Posted by Kenomac

'Seems that after receiving your very nasty PM that you only want yes for an answer.

Then go for it! Please get back to us on how it works out after you spend the $1000.

Or just pm tellie like I said and get the no answer from the pro

[andyalford]

Originally Posted by newhaul

Or just pm tellie like I said and get the no answer from the pro

Yes thanks, I have messaged him.

And in the meantime, found some very interesting technical discussion on this board. For anyone interested in a 'yes' answer:

https://groups.google.com/forum/#!to...ng/1yhPTcgGgLI

The membranes are nominally 12% at 800psi but it seems Spectra are running them at around 600psi to achieve 8 10 or 12% depending on the model.

[buzzstar]

To the OP. Sounds like all you would be doing is using the water that would otherwise be sent overboard through a second membrane, and as previously noted, the water would be far more contaminated and the pressure lower. Would fresh water come out? I have serious doubts, but you might do research to determine the pressure at which the original "waste water" is discharged, and the salinity of that water, along with the maximum salinity the device will handle, to see if there is any chance. IMO, if you are going to spend the money, just install a redundant system. You might want check out the posts in a recent thread using a graphene dive as a sieve instead of reverse osmosis. Not yet commercially available, but it could be worth a few inquiries. Also, take the advice previously offered and contact tellie. Also you might get opinions from Stub and CaptainBill. We all have opinions, usually many, but in the end you need only to act on your own opinions, if you decide to do even that, and it is not a matter or regulation or statute. Keep smiling.

[Crown Royal]

I would try it

[ShaktisBoy]

Why not T off of the high pressure line before entering the membranes assuming you have enough flow rate for both?

[buzzstar]

Originally Posted by ShaktisBoy

Why not T off of the high pressure line before entering the membranes assuming you have enough flow rate for both?

If I were to guess, this might work, and in my not well supported opinion, is probably more likely to do so than the set up I referred to in a previous post. By the way, the technically correct answer to the title question is, yes, but that does not mean it would work.