when sampling for gaseous species combined with particulates.


I have seen teams spend several hours looking for leaks and even the best of us can sometimes miss a problem and be misled. Time spent at the beginning can prevent the wild goose chase at the end.


pment Care, Leak Tests and Inappropriate Repairs ter holder should always be inspected for cracks especially if it is a glass holder, and it


isable to load filters in a clean area. It has been proven to be a good use of time to set vacuum manifold to leak test the filter assembly when it is loaded in a laboratory. This es that the filter can be tightened under vacuum prior to use and it then rarely leaks tested as a full assembly on site. Also, loading filters in a laboratory is easier and less to contamination than on site. The holder will also need to be released under vacuum lly (this latter point does not apply to wingnut type filter housings).


Finally, when on site assemble the whole train, and if the components have been leak tested separately, filter and cold box, then the whole train will probably pass easily. If it does not, set about investigating the source of leak logically. Look for where the bubbles in the solutions are appearing, as this is a good indicator as to the source of the leak. If you think you know where it is, then use a ball stopper to identify whether the train is good up to that point. Finally, if you can’t find the leak be sure to check the umbilical lines because the O- rings in the quick-connects can also leak with time, as they can pick up grit and become scored.


SOURCE TESTING ASSOCIATION I Annual Guide 2019


rn O-ring glassware has helped testing considerably, but the benefits are too easily lost ing glassware from different suppliers. This leads to a mis-match in heights of the gers and the connections to filter holders. In addition, American ball joint sizes are not ompatible with the UK ball joints, hence US and UK glass joints should not be mixed. A fit is not a leak-tight fit.


Method 5 Hot Box and Filter Assembly Filter Assembly


Method 5 Hot Box and


Method 5 Cold Box Assembly


e USA the O-ring glassware is sold with O-rings for single use. but in the UK the O- are typically re-used due to cost. Care should be exercised in their re-use especially trace analysis is involved as they and the grooves in which they sit can be difficult to Re-use also carries the problem that the O-rings will be less good at sealing with time, ng them to fail at the worst possible moment.


Modern O-ring glassware has helped testing considerably, but the benefi ts are too easily lost by using glassware from different suppliers. This leads to a mis-match in heights of the impingers and the connections to fi lter holders. In addition, American ball joint sizes are not fully compatible with the UK ball joints, hence US and UK glass joints should not be mixed. A close fi t is not a leak-tight fi t.


gers should also be used carefully and repaired correctly when damaged. Poor repairs ce poor results. Examples include situations where the jets or the distance to the


gement plates varies affecting the gas scrubbing efficiencies. The size of the jets on nburg Smith (GS) Drip Impingers and the distance the jet is from the impingement e is defined. This is also true for the modified-Greenburg Smith (M-GS) Impinger and


ecified in US EPA Method 5. The GS Impingers with the integral plate are better se they allow some variation in the jacket length. The Impingers which use the bottom jacket as the impingement surface may give some variable results, and this will vary ow rate. This was never the intent with the GS impinger which was designed to test n mines (1922) and Greenburg and Smith may well be turning in their graves.


In the USA the O-ring glassware is sold with O-rings for single use. but in the UK the O-rings are typically re-used due to cost. Care should be exercised in their re-use especially where trace analysis is involved as they and the grooves in which they sit can be diffi cult to clean. Re-use also carries the problem that the O-rings will be less good at sealing with time, allowing them to fail at the worst possible moment.


get the cone of the jacket nor the O-ring insert damp. It makes them stick later. I s use a hot air gun to dry off the surfaces or dry them in a glassware oven. The time


Impingers should also be used carefully and repaired correctly when damaged. Poor repairs produce poor results. Examples include situations where the jets or the distance to the impingement plates varies affecting the gas scrubbing effi ciencies. The size of the jets on Greenburg Smith (GS) Drip Impingers and the distance the jet is from the impingement surface is defi ned. This is also true for the modifi ed-Greenburg Smith (M-GS) Impinger and is specifi ed in US EPA Method 5. The GS Impingers with the integral plate are better because they allow some variation in the jacket length. The Impingers which use the bottom of the jacket as the impingement surface may give some variable results, and this will vary with fl ow rate. This was never the intent with the GS impinger which was designed to test dust in mines (1922) and Greenburg and Smith may well be turning in their graves.


Never get the cone of the jacket nor the O-ring insert damp during assembly. It makes them stick later. I always use a hot air gun to dry off the surfaces or dry them in a glassware oven. The time taken in setting these up always pay dividends when leak tests pass fi rst time. In the USA teams typically go to site with sample trains pre-assembled to aid deployment.


The most common error is connecting the bottle the wrong way around, so always double check prior to turning on the sample pump. Always have a proper set of ball and socket stoppers to investigate leaks, and always leak check the assembled cold boxes with Impingers and solutions prior to the full assembly. This will greatly mitigate leak test failures. I have seen teams spend several hours looking for leaks and even the best of us can sometimes miss a problem and be misled. Time spent at the beginning can prevent the wild goose chase at the end.


An unusual problem can occur with the connector from the umbilical to the glassware which contains a spring-loaded check valve. This valve is to prevent the suck back of liquids if the vacuum pump is turned off prior to releasing the vacuum at the nozzle, or when inserting the sampling probe into a negative pressure duct. However, the valve can jam closed and if it does it creates the impression of a perfect leak check; the giveaway is no flow when you start to sample. It used to be my policy to remove the valve because it was ineffective at preventing suck back, and we rarely encountered highly negative pressure ducts.


L Greenburg and G W Smith Drip Impinger: 1932


In my practice no leak is acceptable, and the gas meter should be totally stationary. If a leak of 2% is thought to be present it usually gets worse and it will be indeterminate as the vacuum on the system changes. So, if using a Method 5 control box at 15” Hg or 380mm Hg there should be no movement on the gas meter. Also check that there is no movement from zero on the ΔH manometer during this period as a double check. Be careful to isolate the


Finally when on site assemble the whole train and if the fi lter and cold box assemblies have been tested separately, then the whole train will probably pass easily. If it does not, set about investigating the source of the leak logically. Look for where the bubbles in the solutions are appearing, as this is a good indicator as to the source of the leak. If you think you know where it is, then use a ball stopper to identify whether the train is good up to that point. Finally, if you can’t fi nd the leak be sure to check the umbilical lines because the O-rings in the quick-connects can also leak with time, as they can pick up grit and become scored.


An unusual problem can occur with the connector from the umbilical to the glassware which contains a spring-loaded check valve. This valve is to prevent the suck back of liquids if the vacuum pump is turned off prior to releasing the vacuum at the nozzle, or when inserting the sampling probe into a negative pressure duct. However, the valve can jam closed and if it does it creates the impression of a perfect leak check; the giveaway is no fl ow when you start to sample. It used to be my policy to remove the valve because it was ineffective at preventing suck back, and we rarely encountered highly negative pressure ducts.


In my practice no leak is acceptable, and the gas meter should be totally stationary. If a leak of 2% is thought to be present it usually gets worse and it will be indeterminate as the vacuum on the system changes. So, if using a Method 5 control box at 15” Hg or 380mm Hg there should be no movement on the gas meter. Also check that there is no movement from zero on the ΔH manometer during this period as a double check. Be careful to isolate the manometer prior to releasing the vacuum or the manometer fl uid will jet downwards and cause havoc. A test should always consist of a pre and post leak check. This is especially true when undertaking a long trial such as one for dioxins. It is a brave (or a foolish) sampler who only tests for leaks at the end of a test!


One of the more recurrent problems is where a system appears to fail a leak check but then suddenly seals. This is often where the top of an impinger and the jacket are not seated properly, and the vacuum being applied pulls the two together, or it is where a fi lter housing is improperly seated on the Tefl on support


L Greenburg and G W Smith Drip Impinger: 1932


Method 5 Cold Box Assembly


8


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