Tightness Testing

Question 1

When performing a Let-by test what pressure should it be set at and for how long do you time it?

Answer 1

Let-by is between 7-10mbars and you time it for 1 minute

Question 2

What is the purpose of a let-by test?

Answer 2

To test the ECV isn’t leaking.

Question 3

What does it mean if the Let-by test fails?

Answer 3

Means gas is leaking through the ECV
i.e. a rise in pressure during let-by

Question 4

What is stabilisation pressure set at and for how long do you stabilise?

Answer 4

Stabilisation is set at 20-21mbars for 1 minute

Question 5

What does the final stage of a tightness test comprise of once let-by and stabilisation has been done and what are you testing?

Answer 5

It comprises of a ‘Final Test’ at 20-21mbar for 2 minutes

Testing tightness of the installtion

i.e. no leaks in pipework or appliances

Question 6

Can new pipework have a permisable drop in pressure?

Answer 6

For new pipework, no permissable drop in pressure is allowed.

Question 7

What is normal operating pressure for a domestic property?

Answer 7

21mbar

Question 8

What pipework diameter can a domestic gas engineer work up to?

Answer 8

35mm

Question 9

What meters can a domestic gas engineer work on?

Answer 9

Up to maximum U16 or G10 which are the largest meters we can work on and anything below these meter types

so…

U6,G4, E6

Question 10

What is the maximum pressure (in Bar) a domestic gas engineer is allowed to work on?

Answer 10

Up to 2bar

or

2bar is 2,000mbar

Question 11

What is the maximum installation volume a gas engineer can work on?

Answer 11

An Installation volume not exceeding 0.035cm2

Question 12

When should a tightness test be performed?

Answer 12

1. New Installations
2. Alterations to, or use of existing installations
3. New extensions to existing pipework
4. Prior to any work on existing installations
5. Where there is a known or suspected gas escape
6. Where there is a complete loss of pressure upstream of the ECV
7. Routine testing of existing installations.
8. Immediately before purging

Question 13

The human eye cannot detect perceptible movement less than what on a u-gauge and what on an electronic gauge?

Answer 13

0. 25mbar on a u-gauge
1. 2mbar on an electronic gauge

Question 14

The size of a permissible drop depends on what?

Answer 14

Size of meter and pipework installation volume

Question 15

What is an AECV and what is an MIV?

Answer 15

AECV = Additional Emergency Control Valve

MIV = Meter Inlet Valve

Question 16

Let-by test fails if the pressure what?

Answer 16

Rises

Question 17

Why do you need to do a stabilisation test?

Answer 17

A stabilisation test is done because the gas pressure in a pipe needs time to stabilise due to temperture fluxuations.

Question 18

When are permissable pressure drops allowed?

Answer 18

Pressure drops are allowed on…

• Existing installations as long as they are within the allowed permisible pressures and there is no smell of gas.

Question 19

If the final stage of a tightness test fails and the pressure drops what does this indicate?

Answer 19

Indicates there is a leak in the installation or appliances.

Question 20

When doing a tightness test and there is a very small pressure loss on an existing installation what should you do?

Answer 20

Refer to the permissible pressure loss chart

If it is an existing installation,
and the pressure loss is within
‘permissible pressure loss chart parameters’
and there is no smell of gas
then this would be a pass.

Question 21

When doing a tightness test and there is a very small pressure loss on a new installation what should you do?

Answer 21

If a new installation then no pressure drop is allowed

Firstly you would need to establish if it is the pipework or an appliance that is leaking?

1. Turn off appliances at appliance isolation valve.
2. Test for tightness again, if there is still a leak it means the pipework is leaking.
3. Find the leak and repair.

Question 22

What are the permissable pressure drops for existing installations for pipework less than or eq. to 28mm?

Answer 22

Ultrasonic Meter

6m3/h or less (E6 meter) or no meter = 8mbar

Diaphragm Meter:

6m3/h or less (U6 or G4 meter) = 4mbar

Diaphragm Meter:
More than 6m3/h but up to & including 16m3/h (U16/G10 meter) = 1mbar

Question 23

What are the permissable pressure drops for existing installations for pipe diameter more than 28mm or less than 35mm?

Answer 23

Ultrasonic Meter

6m3/h or less (E6 meter) or no meter = 4mbar

Diaphragm Meter:

6m3/h or less (U6 or G4 meter) = 2.5mbar

Diaphragm Meter:
More than 6m3/h but up to & including 16m3/h (U16/G10 meter) = 1mbar

Question 24

If an installation being tested does not have a meter
i.e. a flat with a remote meter, then what size pipe on the permissible pressure loss chart should this be based on?

Answer 24

It should always be based on the 28mm or less permissible pressure loss chart.

Basically you can have a higher pressure drop for a flat with no meter (means you would be testing the main meter that supplys that flat) there will always be a larger pressure drop from a shared meter hence a higher tolerence.

Question 25

If Let-by fails what action should you take?

Answer 25

1. Isolate ECV 2. Fit Earth Bonding Leads 3. Disconect ECV anaconder 4. Spray LDF into ECV valve 5. If ECV is leaking reconnect anaconder 6. Call the Gas Supplier

Question 26

What are the 8 visual checks that need to be done on a meter before doing a tightness test?

Answer 26

1. Check ECV falls to correct position and doesnt spin round. 2. Check anaconda is not damaged, twisted, corroided. 3. Check there is an on/off label on the anaconda. 4. Check Regulator is not damaged/ tampered with. 5. Check meter is secure. 6. Check earth bonding is 600mm from upsteam pipe to first tee. 7. Check label present on front of meter 8. Check other there are no other isolation valves.

Question 27

How do you test if pipework or appliances are leaking, and if the pipework is leaking, what would you do?

Answer 27

Test by turning off the appliances at the isolation points, then doing a tightness test, this will establish if there is a leak in the pipework or the appliances. If the pipework is leaking then you have to find the leak and repair it Pressure loss in pipework is not allowed

Question 28

What pressure is supplied to the gas meter?

Answer 28

75mbar

Question 29

Gas being supplied directly to the meter is at 75mbar what device on the meter reduces the pressure down and to what pressure is it reduced to?

Answer 29

The regulator reduces the proessure to 21mbar

Question 30

Before performing a tightness test what should you discuss with the customer?

Answer 30

Advise customer - What you are doing - Ask customer if any issues - There will be a smell of gas - No smoking - All appliances will be turned off

Question 31

If doing a tightness test and the cooker installed in the property is a standalone cooker with a lid what must you do before performing the tightness test and why?

Answer 31

You must shut the lid because the lid has an SSOV valve fitted if the lid is left open the gas is still supplied to the appliance