Installation of reverse osmosis & UV-C system

Reading time 10 minutes

Updated - October 28, 2024

The function of the Reverse osmosis and UV-C system has already been described. The installation in – our – motorhome, Flair 7100 built in 2005, will be described here. The special features of this vehicle version are discussed, where the optimal installation location is and what pitfalls need to be taken into account.

Where should the systems go?

The obvious open spaces are usually already occupied by all sorts of things and are therefore largely out of the question. However, there are also hidden volumes that are predestined for this.

In the kitchen unit behind the sink there are two flaps under which there are waste bin inserts. There is dead space underneath, i.e. behind the drawers and the base cabinet.
This is limited by two wooden panels, which on the one hand form the rear end of the drawer cabinet and on the other hand separate the radiator and the water pipes, including the wastewater piping.

An external flap with external dimensions of 39.5 x 70.0 cm (Thetford service flap size 4) leaves enough space for installation, operation and maintenance of both the osmosis system and the UV-C clarifier including technology and DCDC converter (Victron Orion 12/24 10 A).

In addition, the wastewater piping is directly available for the wastewater from the osmosis system backwashing, as is the cold water pipe for feeding the fresh water into the osmosis system and the osmosis water into the cold water supply pipe of the standard (!) tap.

Only the 12V DC supply line still needs to be laid.

Preparation for service flap installation

Since there is no view from the outside of the cables, etc. behind the planned cutout, a corresponding marking hole must be made from the inside. This requires a long (at least 200 mm) 5 mm drill.

First, the two containers behind the sink must be removed from the flaps. Roughly in the middle you can see a clean rectangular cutout in the rear wooden wall through which water supply pipes and wastewater are routed. At the middle height of the right-hand cutout boundary, the marking hole is drilled at a distance of 2 cm from it (make sure the drill is horizontal) until the drill emerges from the outer skin. This marks the left end of the horizontal on the outside before the beginning of the upper left round corner.

Now draw a horizontal line 85 mm from the lower edge of the cutout from the left wall to the right using a wooden strip about 50 cm long and a thick permanent marker. Along this line is with a Multifunctional device and 270° segment saw blade separated the back board. Shortly before reaching the side wall, sawing with the segment saw blade is stopped and the same is replaced with a straight saw blade. This is placed at a right angle in order to carefully cut through the missing sections up to the respective side wall. The last 15 mm take a little longer because there is a wooden strip behind the board.

Service flap installation – preparations

Cutting templates are included with the service flaps. First, the external dimensions of the complete service flap are cut out along line “A”. This is NOT used to cut out the side wall opening, but simply to check the possible position.

Line “C” represents the cutout for the service flap installation, “B” the cutout for the door insert, which is taken from cutout “C”.
First, cut out along line “C” and transfer the edges to the outer wall with a permanent marker in the determined position in the middle of the determined area “A”. Please note the position of the marking hole as a guide!
The procedure suggested in the instructions with the two positioning holes cannot be followed here, as transferring and marking on the inner wall is not possible.

Making the cutout

After the position has been checked again, the marking can be traced and the wall cut through using the multifunctional tool and the mounted segment saw blade.
However, the wall thickness is greater than the usable depth of the segment saw blade. Therefore, subsequent work must be done with a straight saw blade in order to reach and cut through the rear aluminum and wood layer.

Only (!) the corners are cut through very slowly and carefully with a max. 55 mm deep, fine-toothed metal saw blade and jigsaw. Make sure there is constant contact between the jigsaw base and the outer skin. The foot should be covered with masking tape to avoid scratches on the paint. For additional protection, masking tape can also be stuck to the paint along the cut edges.

The wall thickness of the Flair 7100 is 50 mm, plus the carpet layer on the inside. For this reason, the carpet layer is generally not fully reached by the jigsaw and must be cut through manually with a long carpet knife blade. The round corners can be reworked with a cutter knife, as it is narrower and therefore able to follow the tight curves.

At the border, around the lower fifth of the right vertical edge, you will encounter resistance: the heating pipe. It is about 55 mm deep from the outer skin and would definitely be damaged if a longer jigsaw blade was used!

If the back carpet has been completely cut through, the left side should now be able to be pushed inwards or (using a ruler through the rectangular recess in the rear wooden partition) from the inside outwards. Otherwise it will have to be reworked again. There may be a plastic clamp holder here that fixes one of the two fresh water hoses and needs to be cut with a metal saw blade from a hacksaw (possibly also the retaining screw).

On the right side, the heating pipe is attached with a pipe clamp, which is why it is not possible to give in here. Therefore, enough space must be created between the outer wall and the cutout so that you can loosen the Phillips screw on the pipe clamp using your arm and a small ratchet with a medium-sized Phillips insert. Now you can also move the right side and thus completely remove the section.

Removing the interior wall

The Phillips screws of the right strip of the inner rear wall, which was sawn through from the inside, are now accessible from the outside. These are removed with a medium Phillips screwdriver. Once the strip has been cut through cleanly, the rear wall on the right can be pushed inwards a good bit.
In this way you can also access the left screws, which can also be removed. Now the board is loose, but still too big to get through the opening created on the outside. Therefore, in continuation of the lower left recess, the disturbing right part is sawn off with the multifunctional tool and the panel is then removed.

Before installing and connecting the osmosis and UV-C systems, you should refrain from installing the service flap and temporarily mask the opening if this has to be done outdoors and cannot be completed in one day.

Detail of the service flap insert

To make the flap insert, the template cut along line “B” is positioned in the middle of the wall cutout and the edges are traced with a permanent marker. If necessary, pay attention to motif stickers. Using the jigsaw and a long(!) metal saw blade (shortest length when the jigsaw is retracted > 60 mm), make the cutout following the marking.
Shorter saw blades lead to the rear aluminum/wood composite becoming detached due to incomplete cutting!

The cutout is inserted into the door frame as a test. If there are areas that need to be reworked, this can be done quickly with a fine rasp. As soon as the fit is achieved, the groove in the frame is generously and uninterruptedly filled with body adhesive, the cutout is inserted and firmly pressed. Any adhesive that comes out from behind must be removed immediately without leaving any residue. Glue is also added to the edge of the inner frame and the struts (for larger flap dimensions) and the frame is also pressed in neatly. Before further processing, pay attention to the curing time of the adhesive!

Installation of the osmosis and UV-C system

The DCDC converter (12 V to 24 V) for the osmosis system and the control unit for the UV-C clarifier can now be installed. They are located on the left-hand wall of the kitchen cabinet and are still accessible, but do not interfere with the occasional filter change of the osmosis system or lamp change of the 254 nm UV-C clarifier.

The cover of the PURION UV-C control box can be rotated so that it can also be unscrewed with the operating elements facing downwards for easier access.

The osmosis system is positioned to the right of it, and in front of it the UVC clarifier is attached to two hanger bolts with two clamps to protect against vibrations.

The control panel of the osmosis system was removed from the frame and mounted above the kitchen cupboard. This means you can always keep an eye on the status of the system.

Since the unit is connected to the connected components via a plug-in connection, it is necessary to cut through this and use a 10 x 0.5 mm² Control line to be reconnected – extended. The wires of the control line are numbered from 1 to 9, the tenth line is color coded green and yellow.

The cable assignment is then as follows (from left to right):

Roman numerals indicate the first or second of the duplicate color codes. To differentiate, it is advisable to make appropriate markings on the cable with a permanent marker (one dot / two dots, twice per cable at a distance of about 5 cm. The markings are cut in the middle of the markings. After stripping and crimping the wire end sleeves, the markings are still visible and a correct assignment is therefore given.

• 1 – yellow I – electromagnetic changeover valve (process water/rinsing)
• 2 – blue I – pressure switch 
• 3 – blue II – pressure switch 
• 4 – red I – solenoid valve – waste water OUT
• 5 – green I – 24 V – PLUS (pump) / / black I (electromagnetic valve – waste water IN)
• 6 – yellow II – electromagnetic changeover valve (process water / rinsing)
• 7 – green II – MINUS (pump) / / black II (electromagnetic valve – waste water IN)
• 8 – red II – solenoid valve – waste water OUT
• 9 – white – MINUS (black – power supply / DCDC converter)
• 10 – pink – 24 V – PLUS (red – power supply / DCDC converter)

Pipework

Now the question arises, does the UV-C unit come before or after the osmosis system?

Some manufacturers of osmosis systems speak of a built-in "germ barrier". The osmosis membrane acts as a germ barrier, as it retains all bacteria and viruses with a pore size of just 0.00001 µm.

If the system is not used continuously, as is the case in motorhomes used exclusively for vacations, the germs residing in the osmosis membrane may multiply over time. This provides the answer to the question posed at the beginning: UV-C is placed BEFORE the osmosis system. This kills germs upstream of the system and the filters remain germ-free, even if the water remains in the system for a longer period of time.

It is clever to install ball valves in the respective supply lines, e.g. to prevent flooding when changing the filter (not yet installed in the picture).

A T-piece with ball valve mounted on the outgoing connection allows the pressurized water to be drained outside via a hose routed outside the vehicle.

A note on the screw connection of the (thick) osmosis membrane: depending on the model, the right screw cap is fitted with a sealing O-ring that is either firmly secured in a groove to prevent it from slipping or more or less loosely engages in such a groove and therefore tends to slip out of it when closing and therefore does not seal.
For the latter version, it is helpful to place the system on the left-hand side: this allows you to place the seal in the groove and carefully unscrew the cover until you feel that the O-ring is sealing properly.
A test run in this position should testify to the tightness ...

The other filters have self-sealing screw connections, such as the four vertically installed filters accessible from the front (from right to left - PP filter 10 µm, GAC filter carbon filter, CTO filter activated carbon 5 µm, UF filter 0.02 µm), or direct hose connection, such as the filters located horizontally in front of the osmosis membrane (T33 - activated carbon post-treatment and the yellow cartridge above it, the remineralization stage).

Remineralization is sometimes the subject of controversial debate. The osmosis system also filters out minerals. However, these are needed by the body. It is therefore theoretically logical to add them back in. However, the human organism can only use organic, but not inorganic substances, e.g. through raw food, even if - in the meantime - it is not rich enough. Dietary supplements (NEM) are not booming for nothing and here they certainly make sense as a needs-based supplement. Accordingly, remineralization is not necessary.

Please note: The supplying pressure pump must have sufficient delivery capacity; if necessary, it can also be replaced with a more powerful one!
If a more powerful pump cannot be installed for space reasons here described an alternative.

Three-way valve

The electrically operated 3-way valve (optionally 12 V / 24 V DC or 230 V AC) is used to switch the cold water flow, either via the UV-C/osmosis system or from the water tank directly to the tap and is realized via a pole reversal button with neutral position. By pressing the button in one direction or the other, the water can be pumped via the system or directly from the tank as required. The push-button electrically reverses the two connections of the 3-way valve motor and thus changes the direction of rotation of the motor, enabling either one or the other output of the valve.

Electrical connection

The osmosis system, which is usually permanently supplied with 230 V at home and therefore remains constantly switched on, should also be connected manually via an easily accessible switch. In a motorhome, it is not advisable to keep a pressure pump constantly on standby and maintain water pressure: otherwise, in the event of a leak, the installation area will quickly be under water.

The pump motor of most systems is supplied with 24 V DC via a 230 V AC power supply unit. By using a DCDC converter from 12 V to 24 V as mentioned above, the system can be operated directly via the 12 V DC vehicle electrical system.

The UV-C systems are available with different operating voltages (12 V / 24 V DC or 230 V AC). The 12 V version was selected here. The system is switched on via an illuminated green toggle switch on the control unit (containing the ballast and operating time monitoring for the UV-C lamp). As you generally don't want to have a relatively large technology box in view in the motorhome, the space to the left of the UV-C and osmosis system is ideal, as shown in the photo above.

The disadvantage is that you then have no view of the status LEDs of the UV-C system, and the switch is inaccessible from the inside.
However, it is relatively easy to change this: the switch can be routed inside the kitchen area via two cables that run parallel to the two existing red cables and end in an additional switch, or it can be switched via Smarthome.
As the LEDs are soldered to the control board with long connecting wires, they can be cut there and extended into the desired field of view using cables. This gives you control over the operating states again.

Conclusion

The entire filter chain that available tap water passes through consists of the three-stage pre-filter, 25 µm, 10 µm and 1 µm, followed by the UV-C system and the filters of the osmosis system with 10 µm, 5 µm and 0.02 µm, as well as the osmosis membrane with 0.00001 µm.
Instead of the double 10 µm and 5 µm filters, you could also use 0.5 µm and 0.1 µm. The finer the (pre-)filtration, the longer the service life of the osmosis membrane!

If water of undetermined origin (lake, pond, well, etc.) is used, the filter chain, except for the additional mobile pre-filters such as here described in more detail, identical.
It consists of a 300 µm stainless steel mesh filter basket, a 150 mm polyester sediment filter and a 70 µm stainless steel sediment filter, from where the water is pressure-treated by a membrane pump and fed into the three-stage pre-filtration system described above with 25, µm, 10 µm and 1 µm into the water tank, from where it is fed into the UV-C purification system and the downstream osmosis system.

In this way, water - of any origin - is available at all times in an absolutely sterile state.

Filter change intervals must be observed to maintain sterility. Depending on the degree of contamination of the water, these can also be considerably shorter than the manufacturer's standard intervals!

Objections?

The attentive reader will have noticed that the water filtered to 1 µm will definitely still contain germs. This raises the question: won't the water then be contaminated in the water tank?

Yes, because germs are significantly smaller at just 0.02 ... 0.3 µm. Filters that filter smaller than 0.02 µm, such as the osmosis membrane with 0.00001 µm, have very low flow rates and require correspondingly higher pressures. This results in significantly longer filling times, which can easily last several hours.

However, the bacterial count that may result from longer dwell times of the water in the tank is not critical, provided that the downstream UV-C purification acts with sufficient intensity (joules) and thus not only ensures disinfection, but also the prevention of germination. Photolyase provides. The osmosis system filters out the germs that have been killed off and thus provides germ-free drinking water that is uncontaminated in every respect.

ps If you need personal support in the implementation for a fee, you are welcome to Ticketing make!