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Old 10-06-2017, 16:57   #1
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Deconstructing Spectra's Clark Pump

This is meant to be an explorative thread, aimed at gaining a better understanding of how Spectra's family of Clark pumps function. Until a final consent is reached, all numbers, calculations, and figures should be considered assumptions, unless specifically identified as known (or generally accepted) facts.

The Clark pump is an energy recovering hydraulic pressure intensifier used in the various water maker offerings from Spectra. It is known to be produced in four variations, referred to as the 7%, 10%, 15%, and 20% models. This number represents the product recovery ratio for each pump.

In order to follow along with this discussion, a basic understanding of how the Clark pump is constructed is required, and can easily be found within Spectra's own documentation.

In general, the larger recovery ratio pumps are used in higher capacity water makers. The 7% is used in the 150 model; the 10% from 200 to 400; the 15% in the 700 model; and the 20% in the 1000 model.

Based on research done and published by reliable sources, it has been found that the recovery ratio can be determined as the ratio of the area of the piston rod relative to the area of the cylinder/piston.

From Spectra's documentation, we learn the piston size (and count), for each model:
7%: 1 x 3/4"
10%: 1 x 7/8"
15%: 1 x 1"
20%: 2 x 7/8"

From this, we can easily calculate the area of each piston rod (in square inches):
7%: 0.44
10%: 0.60
15%: 0.79
20%: 1.2

From Spectra documentation on how to deal with a potential problem of swelling pistons, we learn that the piston diameter is 2.735", resulting in it having an area of 5.87 square inches.

If we now calculate the rod to piston area ratio for each pump model, we do not end up with a number that exactly matches the pump model designation. There is especially an anomaly in the one designated as a 15% model:
7%: 7.5%
10%: 10.2%
15%: 13.4%
20%: 20.5%

Let's assume that the calculated numbers reflect the true recovery rate of each pump, as opposed to the designated model number from Spectra.

For a simplistic calculation of pressure intensification ratio (the pressure multiplier), where we ignore any back-pressure on the product side, back-pressure on the brine output side, and any pressure drops in the piping, we can use Ph = Pf / (1-R), where Ph is the high pressure, Pf the feed pressure, and R is the recovery ratio. Using this calculation, with the previously found recovery ratios, we get the following multipliers:
7%: 13.3
10%: 9.77
15%: 7.48
20%: 4.89

With a desired target pressure of, say, 800 PSI, this would result in required feed pressures of:
7%: 60 PSI
10%: 82 PSI
15%: 107 PSI
20%: 164 PSI

With the exception of the 15% pump (calculated using a 13.4% recovery ratio), these numbers align very well with documentation from Spectra, listing the desired input pressures as, respectively: 60-70 (Ventura 150), 60-100 (Cape Horn), 165-180 (Newport 700), and 165-200 (Newport 1000).

I think this is sufficient to get the discussion going. Something doesn't seem quite right with the 15% pump, but I can't put my finger on where I went wrong.
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Old 10-06-2017, 17:44   #2
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Re: Deconstructing Spectra's Clark Pump

Frode,

What is the goal here? If you are trying to understand how your Spectra watermaker works, I think the best approach is to install an inline pressure gauge and an additional pump and experiment with various flows/pressures. Once you have this data, we can discuss further. If I could lay my hands on a Spectra watermaker I would do that for you.

If the goal is to build an efficient energy recovery pump, I think it is a bit challenging. I feel a little uneasy working with high pressure as things tend to blow up unpredictably damaging the boat in the process. It is unlikely that we will come up with something new that has not been thought of already.

If the goal is build a more efficient watermaker, your best bet is with the max recovery approach that would yield between 3 and 4 amps/gallon using a DC motor. Simple and already proven.

I have come across an energy efficient design where a high pressure pump fills the membrane (and an additional high pressure tank) to 800 psi, then operates at low flow equal to the product flow while a small transfer pump circulates the water until 30% recovery is reached, then the water is dumped and the system is refilled with fresh seawater. Such a design mimics the energy recovery approach and is easier to build, although it is still tricky and requires timer control (switch on high pressure pump to pressurize the system, switch off the main pressure pump, run the transfer pump for a minute or so until a certain salinity level is reached, then dump and refill). My estimate is that you should be able to get down to 2A/gallon or better but this is a wild guess.

Basically, it is a small market, I would say less than 5,000 units annually and many cruisers prefer the piece of mind of having professional support from a larger company. May be if we can come up with something small and quiet that requires little installation, it could open up the market. Something similar to the Katadyn 40 but with a pressure intensifier instead of an expensive high pressure pump, fed of a regular pump, ultra quiet, producing 2-3 gpm, selling for $999, just an on/off switch with automatic flush. Must be simple to install, just one connection to the engine intake and one to the engine exhaust. I do not see it today unless it is much higher volume to spread the fixed costs and get lower parts cost.

SV Pizzazz
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Old 10-06-2017, 19:16   #3
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Re: Deconstructing Spectra's Clark Pump

Here is an idea of a zero energy watermaker (not mine, see links below). At depth of 1,800 feet we have 800 psi seawater pressure. Imagine a typical pressure vessel with a membrane (may be end caps with bigger openings). The feed and brine openings are left open. The product opening is fed to a high pressure, empty tank that can withstand 800 psi external pressure (may be a diving cylinder) through a needle valve adjusted to the product flow. You lower this apparatus 1,800 feet (some appropriately sized fishing line), wait for a couple of hours, then pull it up and enjoy the water.

It should work, no?

https://contest.techbriefs.com/2012/...equipment/2620
It is actually patented: https://www.google.com/patents/US20140263005
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Old 10-06-2017, 20:24   #4
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Re: Deconstructing Spectra's Clark Pump

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Originally Posted by Pizzazz View Post
Frode,
What is the goal here?
I'm afraid my goals may be pretty boring. I simply seek to gain understanding - to figure out how everything works. I have a huge water maker on my boat, and vast amounts of energy to run it. Still, I seek something that is quiet, energy efficient, and that works really well, without needing to be handled with silk gloves. I get a kick out of learning, tinkering, and building new and better systems. Besides my 1,000 Amp lithium ion battery charger, and my 1 cm accuracy per all axes positioning system, I'm also highly interested in the concepts of water makers with an energy recovery system. The Clark pump is but one of many that purport to do the same thing, including the one you presented.

I'm buying a Clark pump (or several), simply to change my current system. I retired three months ago, and need to have something to keep mind and hands busy as I'm crossing oceans and enjoying life in remote places where I don't expect there to be external high tech challenges to keep my mind occupied.

I figured there would be plenty of others on this board who would also seek knowledge for the sake of knowledge, without a desire to turn it into a commercial venture. However, knowledge has a funny way of spurring new ideas, leading to new products, whether for self satisfaction or financial benefits.

At this point, all my inventions are done with the express purpose of enhancing my own life. I will share, freely, all the information I gain, but I'm not planning on another commercial venture.
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Old 10-06-2017, 20:30   #5
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Re: Deconstructing Spectra's Clark Pump

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Originally Posted by Pizzazz View Post
Here is an idea of a zero energy watermaker (not mine, see links below).
...
It should work, no?
I will immediately confess to not having read the entire proposal, but it immediately stinks of the perpetuum mobile concepts from the past, also seeking to exploit the concept of "free" energy from the vast pressures in deep water.
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Old 11-06-2017, 08:31   #6
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Re: Deconstructing Spectra's Clark Pump

Quote:
Originally Posted by Pizzazz View Post
Here is an idea of a zero energy watermaker (not mine, see links below). At depth of 1,800 feet we have 800 psi seawater pressure. Imagine a typical pressure vessel with a membrane (may be end caps with bigger openings). The feed and brine openings are left open. The product opening is fed to a high pressure, empty tank that can withstand 800 psi external pressure (may be a diving cylinder) through a needle valve adjusted to the product flow. You lower this apparatus 1,800 feet (some appropriately sized fishing line), wait for a couple of hours, then pull it up and enjoy the water.

It should work, no?

https://contest.techbriefs.com/2012/...equipment/2620
It is actually patented: https://www.google.com/patents/US20140263005

Yes and no. It's always about the energy needed. I skimmed the brief above. I may have missed it but where does it mention flow across the outside of the membrane and how it is achieved. You just can't force salt water through the outside of a membrane using the 800psi from depth then essentially create a constant vacuum on the other side of the membrane and expect the membrane to work for more than a few minutes. They are called cross flow filters for a reason. So a pump would be needed to flow the water on the outside and a pump to keep a constant vacuum on the other side of the membrane. So we are at two pumps, one at the least at a depth of 1,800 feet and one logically on shore where there is grid power to operate both pumps, which begs the question on the above patented system how are these free standing systems off shore powered? 1,800 of depth is usually found fairly far off shore so grid power is going to be a huge issue. Though perhaps the science exists for such a rig the engineering and cost to actually build one that works would be better spent with far more reasonable on far more energy efficient systems already available. Plus how are these 1,800' system going to be serviced? You can't dive that deep. Multi million dollar subs? How much work and energy would it cost to drag these things back to the surface to be serviced? Also the notion that a large ship, much less a Naval ship would pull up to fill up is preposterous. They all have their own water making systems using the already created energy of the ships systems, these are carefully monitored systems and quickly repaired under way. For the cost of the underwater plumbing alone I could easily build a solar powered land based system that would out perform such a system as described above. Now there is a far better answer to the huge amounts of pumping energy wasted in such a system for the pumping requirements that this fellow is unaware of. But he is more than welcomed to contact me and we can discuss my fees and life time residuals to cut his energy use by 80-90%.

PS (some appropriately sized fishing line)???...Man, I want to go fishing with you!
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Old 11-06-2017, 09:19   #7
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Re: Deconstructing Spectra's Clark Pump

Heck with talking about the Spectra mods you are envisioning, I want to see a photo of your 1,000 amp lithium battery charger !
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Old 11-06-2017, 09:31   #8
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Re: Deconstructing Spectra's Clark Pump

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Heck with talking about the Spectra mods you are envisioning, I want to see a photo of your 1,000 amp lithium battery charger !
Not yet, buddy! But, full set of photos, schematics, build instructions, and downloadable controller software will be made available for free when I'm fully satisfied with its operation. It's modular, with 200 Amp stages, each stage capable of working independently of the other stages. I chose 1,000 amps to match it to my 12kW generator.
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Old 11-06-2017, 17:06   #9
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Re: Deconstructing Spectra's Clark Pump

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Originally Posted by Tellie View Post
You just can't force salt water through the outside of a membrane using the 800psi from depth then essentially create a constant vacuum on the other side of the membrane and expect the membrane to work for more than a few minutes. They are called cross flow filters for a reason.
Tellie,

Thank you for the feedback. Are you sure about needing to pump at 800 psi? I believe they are called cross flow filters because one flow supplies pressurized water the other perpendicular flow is the reverse osmosis ion thing. The flow is only needed because we are using a small pressure vessel. If the flow were stopped the membrane lets some fresh water out, the pressure drops and the process stops. However, if you could keep the outside of the membrane (you do not even need a pressure vessel, just the bare membrane) at 800 psi but the product outlet be connected to vacuum, then I think water will flow, as long as the volume of the produced water is small relative to the ocean which is the case .

So, in this case we have just a bare membrane with the product outlet connected to a scuba tank via a tube that can withstand 800 psi external pressure. The whole thing weighs around 25 pounds + another 25 pounds when filled with water. Attach it to a 200 lb fishing line. If using a 21" membrane it would fill up in half an hour. Raise, empty, repeat.

I must be missing something, it cannot be that simple. But I do not believe you need pumps. The work is done through lowering and raising the device. We also need a check valve in the product line (otherwise by the time we raise the device, the water will osmosis back). I am just going to try it!
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Old 11-06-2017, 17:11   #10
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Re: Deconstructing Spectra's Clark Pump

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Originally Posted by Tellie View Post
Yes and no. It's always about the energy needed. I skimmed the brief above. I may have missed it but where does it mention flow across the outside of the membrane and how it is achieved. You just can't force salt water through the outside of a membrane using the 800psi from depth then essentially create a constant vacuum on the other side of the membrane and expect the membrane to work for more than a few minutes. They are called cross flow filters for a reason. So a pump would be needed to flow the water on the outside and a pump to keep a constant vacuum on the other side of the membrane. So we are at two pumps, one at the least at a depth of 1,800 feet and one logically on shore where there is grid power to operate both pumps, which begs the question on the above patented system how are these free standing systems off shore powered? 1,800 of depth is usually found fairly far off shore so grid power is going to be a huge issue. Though perhaps the science exists for such a rig the engineering and cost to actually build one that works would be better spent with far more reasonable on far more energy efficient systems already available. Plus how are these 1,800' system going to be serviced? You can't dive that deep. Multi million dollar subs? How much work and energy would it cost to drag these things back to the surface to be serviced? Also the notion that a large ship, much less a Naval ship would pull up to fill up is preposterous. They all have their own water making systems using the already created energy of the ships systems, these are carefully monitored systems and quickly repaired under way. For the cost of the underwater plumbing alone I could easily build a solar powered land based system that would out perform such a system as described above. Now there is a far better answer to the huge amounts of pumping energy wasted in such a system for the pumping requirements that this fellow is unaware of. But he is more than welcomed to contact me and we can discuss my fees and life time residuals to cut his energy use by 80-90%.

PS (some appropriately sized fishing line)???...Man, I want to go fishing with you!
You are absolutely correct. They are called "cross flow membranes" for a reason. Exactly as you describe was tested and discovered many years ago before polyamide membranes existed. Cellulose acitate and CTA (cellulose tri-acitate ) that would produce permeate​ on chlorinated or non chlorinated water. Hollow fiber construction and used on conductivity of less than 2,500 TDS. The system was connected inline to a household of business (bottling plant). The idea was for zero discharge so there was no discharge. They were relying on the water flow during normal plant hours fun into toilets, faucets, irrigation, and in homes to keep the membranes from plugging up. Overnight, permeate quality suffered, and full tanks of water discarded. It didn't work. Permeate in a hose or tank or whatever at 1,800ft? When permeate back pressure is maxed out at 60psi? It wouldn't be very good permeate if any was made.

Navel ships and even oil platforms have their own Desal systems. Some with plunger pumps and some with axial style pumps. Even the state of the art Duechting pump is used, but so are energy recovery devices such as PX pressure exchangers, turbochargers, and even proton wheels no matter what PD pump is driving the system. Energy recovery is very​ efficient.

Next step in Desal is going to be membranes. We were involved in a pilot program with NanoH2o some year's back that were using a nano technology membrane to reduce the necessary driving pressures. This project was scrapped when the company sold to LG. But this is the direction the industry is moving to.
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Old 11-06-2017, 18:51   #11
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Re: Deconstructing Spectra's Clark Pump

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Next step in Desal is going to be membranes. We were involved in a pilot program with NanoH2o some year's back that were using a nano technology membrane to reduce the necessary driving pressures. This project was scrapped when the company sold to LG. But this is the direction the industry is moving to.
I've worked on about a dozen of these projects over the last few years and about once a month someone will post a link to Graphene or some such new material, but so far nothing is beating the 800psi of the industry gold Standard Dow Membrane. I'm consulting with a project now in Israel that is testing a new membrane with an operating pressure of 400psi. It "works"...but the problem they are having is membrane durability. Small pressure pulsations are damaging the molecular thin layer of active membrane surface area so membrane life is about 30 days of continuous use at the moment. Last I looked at the project budget number they are about 10 million in...anyone got a little R&D dollars to spare?

The next big breakthrough in Sea Water RO will be from the Membranes...just imagine a RO world where like Fresh Water RO all you need is 65psi?
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Old 21-09-2017, 23:28   #12
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Re: Deconstructing Spectra's Clark Pump

Frode, did you get anywhere with this?

I've taken a different approach and I'm trying to build one from the patent, but with a few differences. Ive gone with two discreet cylinders back to back rather than one double ended cylinder with the separating chamber - that's just to make the prototype simpler.

I suspect that the biggest challenge is going to be minimising losses - friction mainly.
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Old 22-09-2017, 02:36   #13
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Re: Deconstructing Spectra's Clark Pump

Greetings and welcome aboard the CF, Gary S.
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Old 22-09-2017, 07:05   #14
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Re: Deconstructing Spectra's Clark Pump

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Frode, did you get anywhere with this?

I've taken a different approach and I'm trying to build one from the patent, but with a few differences. Ive gone with two discreet cylinders back to back rather than one double ended cylinder with the separating chamber - that's just to make the prototype simpler.

I suspect that the biggest challenge is going to be minimising losses - friction mainly.
My current status is that I purchased a 10% Clark pump, put it in a locker, and went to work on a project related to the boat's lithium ion bank. Unfortunately, I have not had time to work further on this.

I probably won't be able to get back to this until I'm sitting on anchor somewhere, about six months from now.
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