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Surface finish of Brass Cylinder Valves ...All that Glitters is not gold

Published on 17-May-2021
Rohit Behani
Rohit Behani

Partner & CEO

I recall my meeting with the factory owner of a reputed tool manufacturer in England 20 years back and our discussion on the quality of taper threads. He informed me that he has come across a made in India cylinder valve having "leave off the mark" on the threads. He further added, with some pride, that even if this defect would not affect the product functionally, it is likely that a buyer in the UK would throw the product in a garbage bin at first sight!!

As consumers, we often judge a product by its finish as we first see and touch it before we put it to use. In the hierarchy of "features" defining product quality, the product's finish sits right on top equally for the consumer and industrial products.

A product having an impeccable surface finish is often, if not always, deemed to be superior to the one which is poorly finished. A perfect surface finish represents the care, pride and diligence with which the product has been manufactured. Depending upon the product, a good surface finish may ensure that the final product may not only look better but last longer.

Brass gas cylinder valves go through a variety of surface treatment processes before they enter the market. At Tekno Valves, we shot blast the valve body forgings to clean the surface and remove sharp edges and an oxide layer formed on the surface. After machining, the valve body and components are degreased using tetrachloroethylene to remove grease, oil, cutting fluid and foreign particles. Most importantly, we do not carry out any "bright-dipping" chemical processes for surface treatment of valve bodies. The implication of this is that Tekno Valve does not look "bright" and "gold", and the WHY NOT is the reason for writing this blog.

With fifty years of experience designing and manufacturing cylinder valves, we have learnt that it is incorrect to judge the quality of the valve by the way it shines.

While "bright dipping" acid treatment looks good once the valves come out of the box, they introduce stress corrosion cracking problems and, because of its surface chemistry, can suffer from unsightly marking if exposed to rainwater.

Further, the acid treatment after machining compromises the surface roughness of the sealing surface, adversely affecting the functionality of valves and requiring higher torques to make the sealing surfaces gas tight.

But as we are a creature of habit, and we always like to make inferences on product quality by how it looks, feel the smoothness of the threads and look for the surface roughness of sealing surfaces and the removal of all sharp edges to make a qualitative assessment before testing the product.

Tip – Request to receive design testing report and type approval certificate for the valve design. Invariably it will filter cylinder valves that have been meticulously designed from the rest.

Someone rightly said, do not judge the book by its cover…

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