Air Vent Positioning

[Paulh_Boats]

Paul H
after leaving the pump is there any downward sections of pipe?

No. Leaving the pump its uphill all the way!   I can vouch for that as the old joints are feeling a stiff today  - but got the panel plumbed and mounted securely with threaded rod at the bottom. 

Its also uphill to the expansion vessel (manufacturer says connection must be below vessel) so manually opening the PRV might vent air. ??

Pete - yes its a simple tap at the highest point.  There are "taps" that open automatically, but they have plastic bits that can melt.

[O MidKnight]

Well done fot the panel fitting Paulh

You may not need a vent in your case then but fit one if you want to. My system has 12 vents including the pump - well they were sorta free

[Paulh_Boats]

O MidKnight

Thanks - it was quite a challenge fitting the panel. Never worked with roof ladders before, never worked with tiles before and making holes in a roof is new skill.    But thanks to help from this forum and yourself I did it!

I'll have a drain right at the bottom, a vent or two at the top in the loft and near the expansion vessel plus Geoff's idea of putting the drain and check valve very close. Also your idea of using 10mm pipe is much easier to connect things up than 15mm. It will be a hybrid 15-10 system and I'll take some pics soon....

-Paul

[dinitro]

Hi

you can buy hand operated radiator vents that do not require a tool to open them.
They can either come as 15mm ie fit into a compression fitting or slightly larger for soldering.

they resemble a cylinder that then forms into a smaller cylinder with threads.  the smaller cylinder terminates
with a small hole.  The smaller cylinder accepts a screw cap which has inside it a small rubber disk.

The profile of the whole vent on  a 15 22 15 T is that you can easily get 22mm armaflex over it with the
vent sticking out.  Of course siting the whole thing inside is best but if only accessible.  If  due to plasterboards etc access is
limited you could get access from the outside via a velux and this may be an option.

dinitro

[O MidKnight]

Had problems in the past with the rubber sticking. Prefer myself the 63v vent made by Prestex ( I think ) or standard rad vent

[dinitro]

Hi O Midknight

Will probably try with some high temp grease.

the only fear with both the standard rad vents and this type of vent is you drop the end piece!
Done this on a couple of rads esp. the ones with the screw with the key at one end that recess into the radiator..
darn things must have fallen though the floor boards... since they had lost their sheen of course impossible to find
and very hard to replace...

probably someone should invent one with a string.... or maybe I should araldite a string to one?

[O MidKnight]

Hello Dinitro

Yes - I agree they are especially hard to find in vermiculite insulation! Greasing the rubber might help short term but I wonder if it would have helped those vents I encountered that had been in ten years or so.   

[Pete]

Hi
Thanks for the explanation. Makes sense to me.

[Niall]

Paulh_Boats wrote:

"There are "taps" that open automatically, but they have plastic bits that can melt."

An option is the Micro-Purg vent http://www.purgomat.de/english/purgo-o-mat-150-heat-en.html.  These are all-metal and specifically designed for solar systems, being rated up to 150 C.  Naturally they cost a lot more than the usual central heating air bottles, but they do work well.  I have had two systems pass 150 during faults and the Micro-Purgs have survived.

Normally I fit them at the highest point, even if that is on the roof, but some folks use air separators with the vent mounted on top http://www.purgomat.de/english/micro-purg-150-solar-en.html.  The separator should be mounted after the panel as the air tends to come out of solution when heated.  On that basis it should be possible to mount the separator & vent in a convenient spot in the loft.  At least, that's what the suppliers say; I haven't seen any particular benefit when using these, but someone else may have more experience with them. They are available from Lili http://lowimpact.org/acatalog/other_components.html.

Niall

[Paulh_Boats]

Niall,

Top tip about the air forming on the hot side. 

I've got the cheapie DIY separator - T joint, 10cm offcut and air bleed.. all of £2. The vertical output pipe (15mm) in the loft is over-bent about 95 degrees, up slighty towards the vent T then curved down to the cylinder via 10mm pipe. That creates a high point for the air to collect before the water heads down to the cylinder...well that's the theory lol 
Being a compulsive fiddler I'll be checking it often... but an auto device is a great feature for yer average customer.


A slightly off-topic question -
Is it considered good practice to make the hole in the felt bigger, so that the pipe insulation can butt up right under the tile?

If the insulation stops at the felt a few inches of pipe will be uninsulated, but I haven't a clue if the bigger hole in the felt makes a rain leak more likely.

thanks
Paul

[Niall]

I usually try to run the insulation through the felt - it should be as continuous as possible and the books say that all joints should be taped, even when they butt together well.  I would agree with this, as when inspecting working installations I have noticed increased warmth at good but un-taped joints.

I wouldn't rely on the felt to provide my waterproofing if possible, but make sure that the insulation has no open ends or joints in the outdoors - else water will sneak in and run down between the Armaflex and the pipe.

N

[ericw]

It seems that using the traditional elbows to connect to the panel there is always a danger that as the panel will be a high point, air may collect there if the water flow rate is insufficient to carry it out.

May I suggest replacing the elbow on the output side with 22x22x15 compression T configured as below to form an inverted sump so that any air that appears in the manifold would be forced down the pipe to be collected in and disposed of in a more convenient (and cooler) place


                                                 _________       sealed off with cap or blanking disc
                                               ||               ||
                                                |    |    |     |
                                                |    |    |     |
                                _________|    |    |     |
                                                     |    |     |
             From Panel                        |    |     |
                               __________    |     |     |
                                                |    |    |     |
                                                |    |    |     |
                                                \    |    |    /
                                                 |X |     | X|          15 mm end with 15-10 reducer
                                                     |     |
                                                        |
                                                        V
                                          To cylinder with air vent on the way

The stop inside the reducer set will need to be removed so the pipe can be pushed through into the top branch of the tee

[The Solar Technician]

The easiest way of protecting an auto air vent is with a 1/4 turn lever valve, thus valving it off. This would allow it to be used during comissioning, but allow it to be removed from the hydraulic circuit when not required, as it could be isolated. simple

but the best way is of course not to fit one.
Try filling the system with an electrically operated pump.
then you can fill and bleed at the same time, as you would when you bleed a cars brakes.

But you are all missing the point.

When you heat a liquid to boiling/stagnation point, the liquid you are using changes form.
The molecules Split.
Just the same as in pan or kettle.
The hydrogen and oxygen molecules split and a gas is formed, creating bubbles.
This is in the form of hydrogen, remmember when you bleed a radiator........ same principle.
In a sealed system these bubbles can not escape and float, or if the pump is on, are pumped around the hydraulic pipeline.
When they get to the pump they collect in the impellor and the pump cavitates.
This will depend upon the activating parameters on the controller you are using and the system pressure you have set.
These bubbles can not be removed with out constant bleeding, but if this is undertaken with an electrically operated pump, a reservoir of anti-freeze mix has to be there to refill.
So in which case you adding fresh liquid so more hydrogen to the system.
There are companies out there which say they can incorporate a form of micro-bubble de-aerator.
All good and well, but same as "purg-o-mat 150" this would then mean the system is now not a sealed system as it now incorporates an air vent which is "automatic"
The problem then arises when the system stagnates and the steam generated arrives at the auto air vent.
The vent is designed to remove air, air is a form of gas, steam is a form of gas, so what tells the air vent that the steam that is now entering it is not to be removed?
The result is the vent or what ever it may be steams.
This vents the system dry, but not only that, with the temperatures in a solar sealed system acheiving well over 200'c.
There is a possibillity some body or thing could be burnt.

Here endeth my teaching studies for today..

The Solar Technician.

[wyleu]

I use a standard 15 mm air vent connected via a hepworth plastic in-line fitting which in turn is fed from the top of the array via 500mm of 15mm pipe with a CAT clip fin on it which is angled at about 10 degrees. the Clip fin keeps he overall temperature down to manageable levels. What this also allows is the detection of air build up by measuring the resistance across the plastic fitting. If theres a circuit there there's water in the system. Very suitable for emergency condition detection.

[bzbrad]

Hi all,

New member here - super web site - learning loads and will be installing a solar system soon.

I would just like to check on Solar Technicians physics though. I didn't think that the water split into hydrogen and oxygen on boiling, water vapor or steam is produced isn't it. Gas is produced in a system from chemical reactions though the net result is the same you don't want to add fresh water to the system to produce more chemical reactions and more gas.