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compare bw air and water leak test


COMPARISON B/W AIR & WATER TEST
INTRODUCTION
One of the first questions that usually arise when talking to customers with little or no previous experience of ir cost effective b

ubble test is doing the work. The reasons are many and this document aims to give these persons an overview of the arguments for selecting show some general remarks and the pros and cons about the different methods and then add some concluding remarks including common misconceptions. Below is a table that shows the approximate leak detection rates with the different methods. Difference with practically being able to detect leaks and theoretically is described further below. This directly shows one common misconception; Air does not find smaller leaks than water, it is actually the opposite, but using water test is not a leak test, it is a way to locate leaks which is further described in the following pages. APPROXIMATE LEAK DETECTION RATES

LEAK RATES ARE IN m.BAR L/SEC

Test using water
General: The bubble method is an inside out method, where the part is first pressurized The part is then submerged down in water Soap solution can be added on the part for easier identification of bubbles This is only a leak search not a leak test Pros: Positive identification of the leak location(s) Cheap system Cons: it is not actually necessary. Objects with large leaks are missed and approved. Products are put in water, hence they become wet, it takes long time to dry. Total leak measurement is NOT possible Very operator dependent, impossible to focus and see all leaks when observing 8 hours a day. When lowering the object air is brought down, which makes it difficult to see if it is leaking or if it just the air that came with the lowering movement that show bubbles. No exact time specifications, some operators only dip the product in the water up and down, then a lot of leaks are missed as it takes time before some leaks to appear as bubbles. Water has a sealing effect on the object if not handled correctly. Sensitivity depends on fluid surface tension and on operator If water is not changed it could cause severe health issues on the operator Lowering objects in water can cause rust on objects If anti-rust agent is used it is not possible to paint the object directly after. The object must first be put in a washing machine and then it has to be dried before the paint can be put on.

12

-145 63 Norsborg, Sverige

-post info@nolek.se

COMPARISON B/W AIR & WATER TEST
Pros and Cons about Pressure decay Test using air

General: A part is put under pressure/vacuum condition A pressure variation is observed over time The detected pressure variation is directly proportional to the leak rate This is a leak test not a leak location/identifying test Pros: Total leak measurement is possible Able to measure to a specified leak rate Able to conduct a real leak test hence a quality control Product is only tested with air, hence products stay dry Less products are thrown away, only the ones that have a larger leak than the specified leak rate will be identified as leaking. Tests are not operator dependent, rather instrument dependent. Cons: This system cost more than a bubble test The test cycle can be longer Not possible to find exact location of leak, hence a good combination is recommended. (Nolek can supply)

CONCLUSION
It is impossible to secure the level of quality with the water method. It is not a quality control since it only works as a leak search and does not replace leak testing with air. That is not to say that the two methods cannot be combined: Use pressure decay to conduct a leak test and certify the quality of the product Use water to identify where the leak is located on the product One does not actually measure more precise with air, one rather measures to the defined leak rate. With the water method it is not possible to define the rate at which it leaks and the most common mistake is that the operator believes that the product is leaking while in fact it is well above the rate at which it is classified to have a leak according to product specifications. Products that are leaking when tested with pressure decay instruments sometimes are leaking when tested in water. The most common fault is that the product is not pressurized before it is lowered in the water and then all leaks will not be identified, especially smaller leaks. Hence, the issue of high dependence of operator arises, the operator has to conduct the test correctly at the same time as he has to be fully focused not to miss bubbles arising. Furthermore, he has to decide how many bubbles that decide if a product is leaking or not, a task which is as impossible as it sounds. The leak rate; 10 mbar.l/sec is theoretically the lowest level where air bubbles are produced in water, below that level the air dissolves in the water without becoming bubbles. A lot of companies with leak rates under this level test products in water but will never see if the product is leaking at the specified level. For example some test gas -6 pipes for air condition applications in water. These products often have a leak rate in the area of 10 mbar.l/sec which means that one is 2-3 decimals from being able to see if the product is leaking or not at the specified level. The conclusion is that one need pressure decay to do a complete quality control on products. The initial investment might be higher but we help companies to leak test their products, leading to a: Saving in cost, being able to deliver to your customers PPM requirements. Increased quality of delivered products when leak testing in the correct way. Improved environment through less leakage and through less transports. Substantial time reduction compared to other leak test methods. Great selling argument
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13

-145 63 Norsborg, Sverige

-post info@nolek.se


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