A game changer watermaker if its as good as claimed.

[Carib]

This would be a brilliant device to have in the grab bag - obviously only intended as a back up. Have you seen the price of the current alternative?

 

[lw395]

The short life of the membrane suggests it's very small and likely more work to pump water through than a larger one?
The low cost seems dubious to me. Two for under £100?
The physical design of it means it can only work on firm level ground quite close to clean (ish) seawater? How many campers and survivalists will that actually help?

 

[rogerthebodger]

I have a Survivor 35 Manual water maker that I purchased second hand several years ago.

There are lots available second hand on E-Bay as they used to be included in the USAF pilot ditch bag.

They do need a service and may be a new membrane which are not cheap.

(Qty 5) Used Survivor 35 Manual, 1.2 gal/hr, Reverse Osmosis Water Desalinator | eBay

 

[dolabriform]

The short life of the membrane suggests it's very small and likely more work to pump water through than a larger one?
The low cost seems dubious to me. Two for under £100?
The physical design of it means it can only work on firm level ground quite close to clean (ish) seawater? How many campers and survivalists will that actually help?

If mine turns up in February I'll post a review !

I see it as emergency backup. Either in the Liferaft grab bag or in case the main water tanks get contaminated. Although I have a General Ecology Nature filter system so it should make the tanks safe, it's always best to have options.

 

[G12]

It's just a cheaper version of the Katadyn sets.....

https://www.enertecmarinesystems.com/product-category/watermakers/katadyn-watermakers/

 

[prv]

The crucial question will be whether it uses the pressure-recovery principle that the Pur / Katadyn one does. That’s what makes hand-pumped desalination feasible, without it you waste too much energy (in the form of pressure in the outlet brine, released uselessly back into the sea). Pressure-recovery instead uses it to assist the next pump stroke.

I understood that this was patented, and the reason the Pur / Katadyn (same device, got sold / renamed) was the only one. But it’s been around for years, so maybe the reason this has come out now is that the patent has expired?

If this new thing doesn’t use pressure recovery then it’s inferior to the existing standard tech.

Pete

 

[Sealong]

For a pump delivering an incompressible fluid (i.e. water):

Power (Watts) = Pressure difference (N/m2) x Flow rate (m3/s)

So with 55 Bar = 55 x 10^5 N/m2
and
2 Litres / hour = 0.002 / 3600 m3/s

Power = 55 x 10^5 * 0.002 / 3600
Power = 3 W
Allowing for inefficiency in transmission, the actual power required is likely to be around 10 - 15 W.
This is achievable with the wrist and arm, but unlikely to bring you out in much of a sweat.

 

[rogerthebodger]

For a pump delivering an incompressible fluid (i.e. water):

Power (Watts) = Pressure difference (N/m2) x Flow rate (m3/s)

So with 55 Bar = 55 x 10^5 N/m2
and
2 Litres / hour = 0.002 / 3600 m3/s

Power = 55 x 10^5 * 0.002 / 3600
Power = 3 W
Allowing for inefficiency in transmission, the actual power required is likely to be around 10 - 15 W.
This is achievable with the wrist and arm, but unlikely to bring you out in much of a sweat.

A normal reverse osmosis water maker has a primary flow rate of several times the output water flow rate. so you need the input raw water flow rate.

 

[AntarcticPilot]

For a pump delivering an incompressible fluid (i.e. water):

Power (Watts) = Pressure difference (N/m2) x Flow rate (m3/s)

So with 55 Bar = 55 x 10^5 N/m2
and
2 Litres / hour = 0.002 / 3600 m3/s

Power = 55 x 10^5 * 0.002 / 3600
Power = 3 W
Allowing for inefficiency in transmission, the actual power required is likely to be around 10 - 15 W.
This is achievable with the wrist and arm, but unlikely to bring you out in much of a sweat.

But it's using seawater at the rate of 20 litres an hour, all of which has to be raised to 55 Bar, raising the power required to 30 watts not allowing for inefficiencies - using the same ratio as you, that could be as much as 150 watts - which will certainly bring you out in a sweat if long continued. If they have a pressure recovery system, then that might be lessened, but there's no hint of it in their diagrams.

 

[Sealong]

A normal reverse osmosis water maker has a primary flow rate of several times the output water flow rate. so you need the input raw water flow rate.

How can the input flow rate not be the same as the outlet ? Unless of course not all of it is raised to the same pressure. In which case the work is done only on the outlet flow.

 

[rogerthebodger]

How can the input flow rate not be the same as the outlet ? Unless of course not all of it is raised to the same pressure. In which case the work is done only on the outlet flow.

Reverse osmosis does not work in the same way as a filter there is always a reject flow of water to flush the contaminants away unlike a filter that retains the contaminants in the filter material.

If this unit does retain the contaminants in the reverse osmosis element no wander the element as such a short like.

This will give you some idea.

Puretec Industrial Water | What is Reverse Osmosis?

 

[mjcoon]

How can the input flow rate not be the same as the outlet ? Unless of course not all of it is raised to the same pressure. In which case the work is done only on the outlet flow.

Because there are two outlets! Even I (with little interest in desalination) know that not all input seawater gets desalinated (where would the salt go?). Just a fraction. The slightly saltier discharge water takes a lot of the energy away with it...

 

[Sealong]

Because there are two outlets! Even I (with little interest in desalination) know that not all input seawater gets desalinated (where would the salt go?). Just a fraction. The slightly saltier discharge water takes a lot of the energy away with it...

And that is my point. The work is only done on the flow that is being forced through the membrane.

 

[rogerthebodger]

And that is my point. The work is only done on the flow that is being forced through the membrane.

You forget the bleed valve that passed the discharge needle valve

Previous discussions of the forum.

diy water maker parts site:forums.ybw.com - Google Search

 

[mikegunn]

And that is my point. The work is only done on the flow that is being forced through the membrane.

I’m afraid not. All the seawater that arrives at the upstream side of the membrane has been raised to high pressure. However approximately 90% of that water is used to flush the membrane surface and is then discarded.
Mike.

 

[Sealong]

I’m afraid not. All the seawater that arrives at the upstream side of the membrane has been raised to high pressure. However approximately 90% of that water is used to flush the membrane surface and is then discarded.
Mike.

Well in that case it's a daft design. Why expend work raising the pressure of 90% of the flow of water only to flush the membrane surface ?

 

[Sealong]

You forget the bleed valve that passed the discharge needle valve

Previous discussions of the forum.

diy water maker parts site:forums.ybw.com - Google Search

And where in your scribble are these two components ?

 

[rogerthebodger]

This is the document I used when I made my water maker

https://sublimesustenance.files.wordpress.com/2012/03/how-to-build-your-own-watermaker.pdf

On page 2 there is a diagram showing the proper setup amd the pressure regulating valve shown in purple maintains the pressure in the membrane that causes water to pass through the membrane thus removing all the salt to make drinking water

Page 7 shows one type of pressure regulation valve and the high pressure gauge that allows correct adjustment.

The diagram on page 1 shows the very basic water maker and it still has a pressure regulation valve in the brine discharge line.

 

[Sealong]

This is the document I used when I made my water maker

https://sublimesustenance.files.wordpress.com/2012/03/how-to-build-your-own-watermaker.pdf

On page 2 there is a diagram showing the proper setup amd the pressure regulating valve shown in purple maintains the pressure in the membrane that causes water to pass through the membrane thus removing all the salt to make drinking water

Page 7 shows one type of pressure regulation valve and the high pressure gauge that allows correct adjustment.

The diagram on page 1 shows the very basic water maker and it still has a pressure regulation valve in the brine discharge line.

Many thanks, that is a most comprehensive document and I am now usefully informed.
However, I think we are straying off course a little.
The point I was attempting to make by applying some very basic physics (in Post No. 27) was that the power input to generate 2 L / hr, with a ∆p of 55 bar was relatively modest and unlikely to work the user up into much of a sweat. I am, or rather was because I have now been enlightened, quite ignorant about the finer design details of a reverse osmosis desalinator. Reworking the calculation based on 20 L/ hr (see AntarticPilot, Post No. 29) does indicate a power requirement in excess of what can be called modest and would certainly bring to question the ability of the user to generate more water than they are losing through perspiration. It would also suggest a power requirement in excess of what a human arm can sustain for an hour or so. A conclusion that in itself begs the questions: 1) is all the water flow raised to 55 bar; or 2) are the specifications actually correct ?

Who knows ? But I think it is informative to make these back-of-envelope calculations to examine claims in a dispassionate manner.

 

[AntarcticPilot]

Many thanks, that is a most comprehensive document and I am now usefully informed.
However, I think we are straying off course a little.
The point I was attempting to make by applying some very basic physics (in Post No. 27) was that the power input to generate 2 L / hr, with a ∆p of 55 bar was relatively modest and unlikely to work the user up into much of a sweat. I am, or rather was because I have now been enlightened, quite ignorant about the finer design details of a reverse osmosis desalinator. Reworking the calculation based on 20 L/ hr (see AntarticPilot, Post No. 29) does indicate a power requirement in excess of what can be called modest and would certainly bring to question the ability of the user to generate more water than they are losing through perspiration. It would also suggest a power requirement in excess of what a human arm can sustain for an hour or so. A conclusion that in itself begs the questions: 1) is all the water flow raised to 55 bar; or 2) are the specifications actually correct ?

Who knows ? But I think it is informative to make these back-of-envelope calculations to examine claims in a dispassionate manner.

Basically, the requirement to pass a lot of seawater arises from the physics of the system. You are using pressure to reverse the normal osmotic flow, which is from less saline to more saline. In order to do that, you need to pressurize the saline side sufficiently to reverse the flow. The pressure required increases linearly with the concentration on the saline side so an increase in the salinity of the saline side increases the required pressure (see Osmotic pressure - Wikipedia). So, if you were to (say) get a yield of 50% of the input stream, it would require an enormously higher pressure to drive the osmosis the "wrong way". That's the real reason why there's a stream of waste seawater - it's salinity has been raised too high for the pressure available to push it through the membrane.

There is a technique to use the "waste" pressure of the output stream to pressurize the input stream, but I gather it's non-trivial and mechanically expensive.