TOPIC:

Rosy:
I'm not saying which is the right interpretation of the urine density experiment, but my first interpretation would be that if you sleep with your head raised it makes breathing easier, which means you sleep more deeply.
When you sleep you produce more of the antidiuretic hormone which controls water loss (or possibly re-uptake, I forget) in the kidneys, so that you lose more urea etc. and less water. I suspect (I fear there aren't any physiologists reading this thread, so I'll have to check it on the physiology forum) that if you sleep more deeply you produce more ADH and therefore urine is denser.
Which would mean that the result would be due to gravity, but rather due to an effect on snot than on blood.
I believe you will find that the negative tension inside the inverted U tube at 20 metres will be far higher than your estimate.


Atmospheric pressure will support a 10m column of water. This will give a vacuum pressure above the water (0Atm) We know that. (I think?)
Atmospheric pressure is about 10^5 Newtons per square metre.
Pressure due to gravity changes linearly with depth in a liquid. In a column 10m high which is in an open jar at the bottom will have a point 10m up where the pressure is 0 bar. You've established that water may but need not cavitate at negative pressures. If it does not then there must be a "pull" from above to support the extra weight of water in the column and the decrease in pressure continues linearly to be -1 Atm at 20m, -2 at 30m, etc, until caviatation occurs and the whole lot falls back to the 10m it can sustain without negative pressure.
The -1Atm pressure at 20m means that there is a pressure difference at that height between the outside atmosphere and the water in the tube of 2Atm or 2*10^5 kN per m2.

By the way, if you've had time to think about getting water out of your inverted tube at the top, which you reckoned a while back you could if you wished design an experiment to do, I'd still be interested to hear about it (or any time you do get time to consider it!)

@Rosy
Actually, you sleep less deeply with the bed inclined, rem sleep is less frequent, dreaming becomes far les frequent. The body generates a substantial amount of additional heat in the inclined position, avoiding the temperature drop off that horizontal sleep causes. More heat = higher evaporation, which inevitably results in the production of denser urine.
Head down tilt on the other hand produces urine of near water density! Which at least proves that renal function requires gravity in order to transport solutes through to the bladder. Head down tilt temperature also fits with the temperature reduction in hibernating bats, and as it is used to simulate the harmful effects of micro-gravity on astronauts, it has been thoroughly investigated, with huge amounts of literature available on the internet.

Dave:
Isn't REM sleep an indicator of light sleep - deep sleep happening in between the episodes of REM/dream sleep?

It may indicate that renal function is assisted by gravity, but it certainly doesn't proove gravity is required for solutes to be moved to the bladder. If it was the whole story then astronaughts would be dead after a few days in space...

It is possible that a lot of sleep problems could be assisted by altering the angle of the bed - this will have lots of effects like altering snoring, altering how hard the heart has to work, which will have lots of subsequent effects... the human body is a horribly complex system so making niave conclusions from simple experiments is a little dangerous

Must say I have followed most of this thread and it's exhausting to read....like a couple arguing about the same thing but not hearing each other. Andrew is right....TRY it first and witness it. Then comment. The opposition doesn't want to try it....they use everything in their argumentative power to shoot it down. Isn't this the classic historical argument. Right from Semmelweis to countless others who opposed convention and were attacked for it, the story is the same. But we lack an accurate explanation for it. Yet it has been explained in detail by Wilhelm Reich MD. He watched scientists observing spontaneous movement of protoplasm and interpreting it in a way that suited their biophysical makeup...in other words...when we observe nature we see it through our own emotional state, and because most of us have what is called emotional plague...problems ensue.
Wish you luck Andrew..trying to convince convention, but with issues that affect our own life force you need a lot of it. There is absolutely no way everyone will agree to something that affects our energy state. It's the way the world works. When I first read your theory I KNEW you were right instantly...from what I have studied and seen. The very next day I was sleeping inclined. I doubt I will go back to flat sleeping ever. Now I read many articles against it...some claiming it may degrade sleep etc etc...all by people who have not tried it am sure.

@Rosy

Atmospheric pressure will support a 10m column of water. This will give a vacuum pressure above the water (0Atm) We know that. (I think?)

If you are referring to the barometer type experiment, the only reason the water remained in the tube was because of the ability of water to stick to the top of the capped tube and the friction to the internal walls of the tube, again adhesive (adhesive quality of water) Atmospheric pressure does contribute to the experiment but not as much as believed, demonstrated by the inverted U tube, which relies on the cohesive force of water, more than doubling the height achieved and therefore indicating that adhesion was the principle factor in the barometer type experiment. When the water level goes below the 10 M level in the Barometer type experiment, it is then supported by a vacuum.

In the Inverted U tube experiment, there is twice the weight applied to the column of water suspended over the raised middle of the tube, and therefore twice the amount of tension is applied to the water inside the tube, yet it remains relatively stable providing the gas has been removed from the water by pre-boiling it.

The pull from above is balanced by the equal opposing pull on the opposite side of the tube, which therefore is a not actually a pull from above, more an increase in tension.
Again atmospheric pressure plays a part but not as much as previously thought. More, the Cohesive strength of water is tested against the adhesive strength of water + the additional friction caused by the additional adhesion to the doubling of the length of tube compared to the single vertical tube.

I conducted another experiment at 2 metres elevation, This involved 3 lengths of tube connected to a central T Junction, one length was longer than the other 2, to allow the open end to be doubled back on itself into a U shape, again with the end open and the water level inside to be at the same level as the water level in the jug which contained the other two open ends of the triple conduit. The U ended tube was allowed to fall below the water level in the jug containing the otehr two open tube ends ends. The whole experiment was filled with pre-boiled water and great care was taken to make sure there were no leaky joins where air could be sucked in.

What would you, or anyone else reading this expect to happen to the water in the end exposed to the atmosphere via the U shaped exit point, and the central T junction was elevated to 2 metres vertical?

With regards to constructing an experiment to show that water can be excreted from a tubular construction, Eduard Strasburger already did it by killing the tree and observing water transpiring from the leaves for three weeks after the death of every living cell in the tree, making the trees tubular structure a perfect example of your challenge! And in doing so concluded that bulk flow was not a living process, but a Physical non-living process! I am tempted to repeat his truly fascinating experiments myself.


Andrew

I have been reading this thread and thought I might add that I was at the London International Inventions show in 97 and saw the experiment on display at Andrew’s stand. It was remarkable. From what I remember he had a dark red coloured liquid, which was salty water and dye in a simple loop of tubing suspended on a board with bags. Although I didn’t fully understand the explanations he gave, the water did appear to be flowing up and down.

He was showing a bed that was tilted. I didn’t stay to the end of the show to see if he won anything for his invention, but the experiment was impressive.

Terrence

Rosy:
Andrew, I hope I'm about to explain some things you already know. But it's not at all clear from your posts that you do understand this stuff. I'm not going to consider the effects of introducing different densities of liquid, because that merely confuses the issue.
I don't think you should be disagreeing with me on any of the points I make here.

The basic point about a liquid such as water is that the pressure at a given depth is constant for any interconected bodies of water (where each is free to flow into the other.
So if equal pressures act on both side of a U tube open at both ends, the water in the two tubes will be at the same level.

If we then take out some of the air on one side (say reduce the pressure to half an atmosphere) then the water on that side will be pushed through the system by the air pressure on the other side until the system is balanced again. At this point, the pressure in the water on the other (lower pressure) side, at the same level, will also be 1 Atm. This will be due to (i) a pressure of 0.5 Atm from the gas and (ii) an extra weight of water, which will be enough to give 50kPa per square metre (as water weighs in at 1000kg per metre cubed, so a metre depth of water exerts a pressure of about 100N per square metre=100Pa) so the depth of the water will be 5m higher on one side than the other for a 0.5Atm air pressure difference.

When the water level goes below the 10 M level in the Barometer type experiment, it is then supported by a vacuum.

This is entirely untrue. The water is not supported by the vacuum in a barometer, it is pushed up by air pressure at the water level of the open vessel which gets it up to a height of 10m under compression. The vacuum cannot provide *any* force on or against *anything* because THERE'S NOTHING THERE, it's just a total absence.

Up to 10m, nothing has to be supported under tension *at all* because it's all happening at positive pressure.

In the Inverted U tube experiment, there is twice the weight applied to the column of water suspended over the raised middle of the tube, and therefore twice the amount of tension is applied to the water inside the tube, yet it remains relatively stable providing the gas has been removed from the water by pre-boiling it.

Um, no. In an inverted U-tube less than 10m in height there is no tension at all, it's all happening under positive pressure, just less than atmospheric. There's quite a large difference between the two [1] (provided there's no other way of air at atmospheric pressure seeping into the system). The pressure in the two tubes at any given depth will be the same. If there is space for it to do so, the water wants to move from high to lower pressure, which is how a syphon works- if pressure is 1Atm at a point on one side of the system and at some open point lower down on the other side there will be a positive pressure greater than 1Atm at that point. In which case, if it is open to the air, water will be pushed out of the system against the 1Atm pressure.
Above 10m, provided no cavitation occurs, the same will apply. Pressure falls constantly all the way up, and negative pressures "pull" exactly the same in all directions... against the walls of the tube, against neighbouring "bits" of water and so on.

Strasburger already did it by killing the tree and observing water transpiring from the leaves for three weeks

My point is that I think that your demonstration system requires more weight coming down than going up (weight of water plus weight of solution). This is very obviously not true of a tree and doubly untrue of Strasburger's dead tree which is no longer synthesising sugars.
If you can't build a demonstration then an account of a back-of-an-envelope calculation accounting for the energy and mass transferred (what's going where and what's powering it) might serve equally well to convince me.

What would you, or anyone else reading this expect to happen to the water in the end exposed to the atmosphere via the U shaped exit point, and the central T junction was elevated to 2 metres vertical?

I have no idea... I don't understand your description. Any chance of a diagram?

@Rosy

I forgot to add that Strasburger's experiment (killing the tree) caused a cascade of solutes to flow down from the inevitable decay of the foliage and internal cells. According to my theory this would be more than enough to cause the flow and return to carry on for three weeks or more. The solutes did not vanish suddenly along with the death of the tree, they remained at an elevated point and were released slowly. I think Strasburger may have even noticed an increase in the circulation of the dead tree during the rapid release of stored sugars and salts.

I really don't relish killing a tree for science to test this, being a tree hugger by nature, I like planting trees not destroying them.

If i purchase a digital camera and video the experiments would this be acceptable to you and others? Seeing as no one can be bothered to repeat them. I have the original Brixham exp on video also, maybe I can find a way to load it on to a website.

Andrew

Dave:

A simple thought experiment for you to consider Imagine the inverted U tube experiment set up, but this time, the two open ends are submerged in one sealed container, with the water level afording some air space above it. And it has all the pressure removed eliminating any positive pressure or influence from the atmosphere.

By eliminating any positive pressure do you mean carrying out the whole experiment in a vacuum? as otherwise there will allways be a positive pressure. You can't do this with open ends to the tube as it would cause the water to evaporate at the ends quite quickly...

:Prediction, the water column will remain intact. What do you think? B.T.W thinking about a way of testing this one to settle an argument.

If you could somehow do it without exposing the surfaces to a vaccum and none of the surfaces were hydrophobic to act as nucleation sites it probably would remain intact - if you ignore the bottom 10m of your experiment that is essentially what you have done.

You could build your 2m loop and attach syringes to the end and pull on the syringes with a force of 100 000N x Area of syringe in square meters (so for a syringe with an area of 1cm2 apply a force of 10N or about 1kg. This would be equivalent to doing the experiment in a vacuum as the weights on the syringes should be compensating for atmospheric pressure.

As a check try it with and without a tiny bubble in the system, if when you add the bubble the weights pull the plungers out but when you don't have a bubble they don't, I think it has shown what you want to.

quote:In the case of the barometer type experiment, "Thought experiment again unfortunately" removing the poitive pressure in this experiment by sucking the air out of the beaker containing the water with the open end of the capped water filled tube will indeed cause the water to be pulled from the top of the capped tube at a much lower height than ten metres. But this does not prove that the pressure was the only force supporting it. It suggests that the increased downward force of the water has severed the hydrogen bonds to the capped glass tube.

If you are using very clean and boiled water I expect that you could support a column higher than 10m in a glass tube, and I am sure it is possible using the tubes you do - as long as you can fill the end of the tube with no bubble or with something that has holes so small that sufrace tension can support the pressure - a tree.

The ten metres thing does however hold if you are using large tubes with dirty and unboiled water as once there is a bubble the water will cavitate if there is a negative absolute pressure.

But this is all dead standard cohesion theory...

I was trying to refer to the way a syringe pulls water up, even when there is air space directly in front of the plunger. The absence of pressure if you like is sufficient to draw water up acting upon its surface, so why do you think the vacuum is any different to the suction caused by the plunger in a syringe?

The reason that a syringe can suck even with a bubble in it is that everything is under atmospheric pressure 100 000Pa - the equivalent of 10m of water.

so if the water in the syringe is under a pressure of 100 000Pa and the fluid in the syringe is under pressure of 90 000Pa there will be a NET force towards the syringe and liquid will flow in, without having a negative absolute pressure anywhere.

I think you will find that the syringe will not suck if there is a bubble and you are working against more than 10m of head - again you are in a good position to try this.

@Dave, you have made some interesting points, and I have taken on board your idea about a syringe and a kilo weight. Great idea if the syringe can deal with a kilo force in the opposite direction to its designed function, but its certainly worth a try.

By the way, if the inverted tube is at 2 metres and the ends submerged in water at equal lengths, filling one bottle higher than the other causes it to flow to the other bottle as expected. From what I remember this was not the case at over the 33 feet limit. But I will have to test again at some point to make certain. Also, at 2 metres using the salt, it does not return to the other side because of the increased density of the salt receiving side. I have not observed the coloured salt solution flowing back up the tube once it has reached the bottle and the tube contains clean water. Also, you can regulate the flow by altering the density on the rising side bottle. This is important, because it suggests a mechanism for acid rain to kill trees by altering the density of the ground water by dissolving a greater amount of minerals from the soil. It should be easy to test this by adding salt solution to the soil, and then adding distilled water to compensate for the increased salt to see if it allows the plant or tree to recover. This also fits with overfeeding plants and killing them.

Thanks for the suggestions

Andrew

Dave:

Cool, just be a bit careful about the design of your experiment, as if you are attempting to distinguish between two hypothesies you have to be careful that the result will be difficult in the two hypothesies. I think adding a lot of salt to the ground would kill the tree in the conventional model as it would tend to dessicate the roots by osmosis...

Out of interest what do you mean by return to the other side? It is hard to describe this sort of thing without a diagram... Do you mean that in teh long tube the flow overshoots and then afterwards flows backwards for a bit?

The last post was refering to the single looped tube exp.

According to the results in the single loop tube, it should only require a relatively small amount of salt to upset the flow, when added to the rising tube side. However, the tree has a fair amount of sugars and minerals in the sap and stored in the leaves, branches and trunk. So the salt may cause the leaves to wilt, but it may not kill the tree for a long time. just wandering if anyone has done something similar with trees and posted on the net?

Trees the key to beating salinity
DAFF04/175M 18 August 2004

The Australian Government's Natural Heritage Trust will invest $2.9 million over two years to develop commercial environmental forestry (CEF) that will address salinity.

Speaking at a regional forest investment workshop in Morwell, Australian Forestry and Conservation Minister Senator Ian Macdonald said the CEF program developed farm forestry systems that reduced salinity while delivering commercial returns.

"It is about linking the commercial to the environmental to develop long-term agricultural business options for farmers affected by salinity," Senator Macdonald said.

"When adopted, CEF will also benefit the broader community by not only reducing salinity in the Murray system, but also by protecting water quality and biodiversity. The CEF project supports private and public outcomes for regional catchment management groups and private investors to deliver benefits."

The CEF project began in 2003, and is a major collaboration between CSIRO and the Australian Government Department of Agriculture, Fisheries and Forestry. Other partners include the National Association of Forest Industries, the Murray Darling Basin Commission and the Victorian Department of Primary Industries.

The project partners will invest more than $4 million in 2004-05, and plan further investment in 2005-06.

The project is focussed initially on a pilot in the Goulburn Broken Catchment where salinity is a major problem, and the Catchment Management Authority (CMA) has targeted forestry as a potential solution. The CMA is an active partner in the project and is holding community forums to involve landholders.

The project has identified those areas in the catchment where forestry will reduce salinity without stressing river flows. These areas are typically found where rainfall and growth rates are lower than in traditional plantation areas. CSIRO is undertaking research to reduce investor risk by identifying species with commercial potential for these lower rainfall areas and developing growth predictions for them.

The project is also quantifying the other environmental benefits of farm forestry of interest to regional NRM groups and governments. These include biodiversity conservation, carbon sequestration and erosion control.

"This new funding of $2.9 million comes on the back of initial seed funding of $550,000 provided last year," Senator Macdonald said.
www.mffc.gov.au/releases/2004/04175m.html

Response of orchard 'Washington Navel' orange, Citrus sinensis (L.) Osbeck, to saline irrigation water. II. Flowering, fruit set and fruit growth.

H Howie and J Lloyd

Abstract
Flowering, fruit set and fruit growth of 'Washington Navel' orange fruit was monitored on 24-year-old Citrus sinensis trees on Sweet orange rootstocks that had been irrigated with either 5 or 20 mol m-3 NaCl for 5 years preceding measurements.Trees irrigated with high salinity water had reduced flowering intensities and lower rates of fruit set. This resulted in final fruit numbers for trees irrigated with 20 mol m-3 being 38% those of trees irrigated with 5 mol m-3 NaCl. Final fruit numbers were quantitatively related to canopy leaf area for both salinity treatments.Despite little difference between trees in terms of leaf area/fruit number ratio, slower rates of fruit growth were initially observed on high salinity trees. This effect was not apparent during the latter stages of fruit development. Consequently, fruit on trees irrigated with 20 mol m-3 NaCl grew to the same size as fruit on trees irrigated with 5 mol m-3 NaCl, but achieved this size at a later date. Measurements of Brix/acid ratios showed that fruit on high salinity trees reached maturity standards 25 days after fruit on low salinity trees.Unimpaired growth of fruit on high salinity trees during summer and autumn occurred, despite appreciable leaf abscission, suggesting that reserve carbohydrate was utilized for growth during this period. Twigs on high salinity trees had much reduced starch content at the time of floral differentiation in winter. Twig starch content and extent of floral differentiation varied in a similar way when examined as a function of leaf abscission. This suggests that reduced flowering and fruit set in salinized citrus trees is due to low levels of reserve starch, most of which has been utilized to support fruit growth in the absence of carbohydrate production during summer and autumn.

Keywords: Oranges, irrigation, water, salinity, responses, fruits, set, development, flowers, initiation, Carbohydrates, metabolism, Polysaccharides, Flowering, growth, Maturation, subtropical fruits, citrus fruits, fruit crops, Citrus, Australia, Rutaceae, Sapindales, dicotyledons, angiosperms, Spermatophyta, plants, Australasia, Oceania, 2180,

Australian Journal of Agricultural Research 40(2) 371 - 380
www.publish.csiro.au/nid/40/paper/AR9890371.htm

Salinity and drought stress effects on foliar ion concentration, water relations, and photosynthetic characteristics of orchard citrus.

JP Syvertsen, J Lloyd and PE Kriedemann

Abstract
Effects of salinity and drought stress on foliar ion concentration, water relations and net gas exchange were evaluated in mature Valencia orange trees (Citrus sinensis [L.] Osbeck) on Poncirus trifoliata L. Raf. (Tri) or sweet orange (C. sinensis, Swt) rootstocks at Dareton on the Murray River in New South Wales. Trees had been irrigated with river water which averaged 4 mol m-3 chloride (Cl-) or with river water plus NaCl to produce 10, 14 or 20 mol m-3 Cl- during the previous 3 years. Chloride concentrations in leaves of trees on Tri were significantly higher than those on Swt rootstock. Foliar sodium (Na+) and Cl- concentrations increased and potassium (K+) concentrations decreased as leaves aged, especially under irrigation with 20 mol m-3 Cl-. Leaf osmotic potential was reduced as leaves matured and also by high salinity so that reductions in leaf water potential were offset. Mature leaves had a lower stomatal conductances and higher water use efficiency than young leaves. After 2 months of withholding irrigation water, leaves of low salinity trees on Tri rootstock had higher rates of net gas exchange than those on Swt rootstock, indicating rootstock-affected drought tolerance. Previous treatment with 20 mol m-3 Cl- lowered leaf area index of all trees by more than 50%, and resulted in greater reserves of soil moisture under partially defoliated trees after the drought treatment. This was reflected in more rapid evening recovery of leaf water potential and less severe reductions in net gas exchange after drought treatment in high salinity trees on Swt rootstock. High salinity plus drought stress increased Na+ content of leaves on Swt, but not on Tri rootstocks. Drought stress had no additive effect, with high salinity on osmotic potential of mature leaves. Thus, the salinity-induced reduction in leaf area appeared to be independent of the Cl- exclusion capability of the rootstock and decreased the effects of subsequent drought stress on leaf water relations and net gas exchange.

Keywords: Oranges, salinity, responses, rootstock scion
www.publish.csiro.au/nid/40/paper/AR9880619.htm

Salinity

Cause

Salinity damage is caused by the accumulation of toxic levels of salts (sodium and/or chloride) in the tree. This usually arises from the use of saline irrigation water or the presence of a saline watertable within or just below the rootzone.

Symptoms

The severity of symptoms increases with the concentration of salts accumulated in the soil and/or trees. Loss of tree vigour is a major symptom of salinity. Trees affected by salinity generally show water stress before they should, ie when soil moisture content appears adequate. This is particularly the case where salt has accumulated in the soil.
Marginal leaf burn, particularly towards the tips, is characteristic of salinity. Leaves tend to be cupped. Premature drop of a proportion of the older leaves may occur along shoots.
When cut off, the branches of salt affected trees have discoloured heartwood.
In severe cases salinity causes tree death.

Control

Leaf nutrient analysis is a useful means of detecting the development of salinity problems. Annual leaf analysis will reveal the trend in leaf sodium and chloride levels. If levels are increasing the cause of this should be investigated. Bear in mind that higher levels can be expected in low rainfall seasons and in years of higher than normal river salinities.
The water used for irrigation in the Riverland is relatively saline, normally in the range 400 to 800 EC. With adequate irrigation management and good drainage, these levels of water salinity need not substantially affect stone and pome fruit production.
Leaching of salts through the soil profile is a necessary part of irrigation in the Riverland to prevent salt accumulation in the rootzone.
For further information refer to the irrigation section.



Knowledge of the problem?
Observations of increasing land and stream salinity were first reported many years ago. In 1907 Government Analyst E. A. Mann suspected that there was a relationship between clearing and the development of land salinity.

In 1902, 8,000 ha of trees in the Mundaring Weir catchment were ringbarked to increase run-off. Salinity in the weir increased, and in 1909 it was recommended that regrowth be encouraged and replanting undertaken. This was done and salinity levels fell.

Increasing salinity in railway dams used to supply water to steam engines was also observed. A railway engineer, W. E. Wood, collated and analysed the early data and with the publication of his paper in 1924 the relationship between clearing and increased land and stream salinity was unequivocally established.
agspsrv34.agric.wa.gov.au/environment/sa...nity_at_a_glance.htm

Dave, this does appear to fit with the saline regulation of the tubular experiment, where the saline sollution isadded to the rising tube side bottle.

But more to the point, it was because of my interest in irrigating deserts and reforesting them that I considered how the trees were dealing with salts in the first place. I have contacted the Australian Government and several experts on desertification many times over the years, but failed to touch a nerve. Now trees are being recognised as valuable desalination plants.

This is good news for me. I have been shouting this message at them since 1993. "Plant Trees to reduce salinity in the ground water" I am curently shouting a similar message to the people in Thailand, who are experiencing one of the worst droughts in their History.
www.thaivisa.com/forum/index.php?act=Pos...&t=29285&qpid=358136

Rabeldin:
Mangrove trees, which grow in salt water, so something opposite. They take in salty water and deposit salt crystals on the surface of their leaves. Surely, the difference in ion concentration is a crucial factor in both situations.

R A Beldin,
Improbable Statistician

@ R.A. Beldin

Mangrove trees are able to restrict the amount of salt they take in and the salts found on the leaves are a result of evaporation, re-concentrating the salts. The difference in ion concentrations is indeed a crucial factor in all situations. Wherever a concentration takes place due to evaporation there is an obvious alteration of density in the fluids that are shedding water. There has to be! Denser solutes at the evaporation points will inevitably be acted upon by gravity and there goes that for every action there is a reaction again. Gravity will pull the denser solution down and the negative tension behind the falling sap will draw up less concentrated solution as a return flow, much the same as a flow and return system in a central heating boiler, which uses heat to alter density on the rising side and the cooled water becomes denser so provides the return flow. Having fitted this type of boiler it contributed to the discovery. Flow and return hot water supply drawings. www.gasman.fsbusiness.co.uk/system_basics.htm www.ecoplusonline.com/images/Fig5_70.gif