Pressure testing central heating system

chris_n

60 PSI is plenty of pressure to cause big problems and serious injury when it is a gas that is under pressure. 

cerebus

Section62 said:

cerebus said:

Never understood why people air pressure test a water filled system, firstly if anything shoots off like an endstop during the test , it could be curtains for the poor sod who gets hit in the head with it I.e. it's incredibly dangerous

Secondly air molecules are smaller than water molecules so if you get an leak during an air pressure test that same leak probably won't show up on a water pressure test 

Air testing is done for exactly that reason - the air test will show up any leaks in more borderline cases, and generally do so quicker than with a water test.

It's also usually easier to clean up after a failed air test than it is a failed water test.

Any pressurised system failing poses a safety risk. The higher the pressure, the greater the risk.  As an air test may give a 'fail' result at a lower pressure, it follows that done with due caution, an air test may be less risky than a water test.

The key thing is adopting a safe method of working - i.e. don't sit/stand in the potential path of something that might shoot off.  That applies whatever medium is being used to pressure test the system.

Why would you want to show up any air leaks in borderline cases when the system will be filled with water? 

With the amount of joints in a typical central heating system I would not want to be anywhere near it if it lets  go - ill stick with water pressure testing and risk a minor leak from the sealed system if anything lets go, I value my life and its much easier to find a water leak in "borderline" cases 

Section62

cerebus said:

Section62 said:

cerebus said:

Never understood why people air pressure test a water filled system, firstly if anything shoots off like an endstop during the test , it could be curtains for the poor sod who gets hit in the head with it I.e. it's incredibly dangerous

Secondly air molecules are smaller than water molecules so if you get an leak during an air pressure test that same leak probably won't show up on a water pressure test 

Air testing is done for exactly that reason - the air test will show up any leaks in more borderline cases, and generally do so quicker than with a water test.

It's also usually easier to clean up after a failed air test than it is a failed water test.

Any pressurised system failing poses a safety risk. The higher the pressure, the greater the risk.  As an air test may give a 'fail' result at a lower pressure, it follows that done with due caution, an air test may be less risky than a water test.

The key thing is adopting a safe method of working - i.e. don't sit/stand in the potential path of something that might shoot off.  That applies whatever medium is being used to pressure test the system.

Why would you want to show up any air leaks in borderline cases when the system will be filled with water? 

With the amount of joints in a typical central heating system I would not want to be anywhere near it if it lets  go - ill stick with water pressure testing and risk a minor leak from the sealed system if anything lets go, I value my life and its much easier to find a water leak in "borderline" cases 

It depends whether you are testing the system to find out if there are any leaks, or happy to convince yourself there are no water leaks at the point in time you are testing.

If air is escaping from the system then there is a leak.  Whilst perhaps not able to pass water at that point in time, it wouldn't be unreasonable to expect corrosion may enlarge the point of leakage to the extent where water will start leaking out.  Hence "borderline".  The point being that water may not leak out in these cases and therefore the leak might go undetected at the time the test is carried out.

There are also cases where if air can leak out, then air can leak in.  And as there are situations where a system which allows air to leak in can be problematic, carrying out an air test may be the only way of getting a meaningful test result.

You asked "Never understood why people air pressure test a water filled system".  I answered your question.  Nobody is suggesting you should carry out air testing, and if you don't feel confident doing so it wouldn't be sensible to start.  Pressure testing any system can be dangerous and shouldn't be attempted by anyone without the required skills.