Durability of Nylon 11 coated disc (butterfly valve)

[DAquilina]

I am considering accepting a butterfly valve that has a nylon 11 coated disc in a hydronic piping specification (for commercial/institutional HVAC applications).

Currently, our specification calls for a bronze disc and I am considering expanding that to include a nylon coated disc.

My question to the forum is: Has anyone experienced the problem of the nylon coating breaking off, requiring valve replacement and significant damage to the hyrdronic system?

This valve will be in a hydronic system, so it may see glycol or water treatment chemicals.


Thank you and regards,
Dave

 

[gerhardl]

I have myself no relevant experience for nylon coated valves, and will not comment on this directly, but will suggest that you 'sharpen' your quality description and research before you accept this new valve:

1. producer to give relevant positive references from long-term installations you can check yourself.

2. Exact description of coating and construction. As known 'nylon' was originally a trade-name for a DuPont patented polymer, and newer variations by others are different , but behaving about the same, but some variations / similar constructions may prove better (??? delrin ??? is this a nylon? or (cheaper? PTFE?)

3. Coating thickness, stem material, stem cover, bearing, disc (metal) material, mechanical details and strength together with exact chemical conditions during lifetime for media exposed parts will influence on cost/ lifetime considerations.

3. If this offer has come 'out of the blue' ask your normal supplier and at least one other competitor for competing offers, ask all to include references,expected lifetime and arguments for the construction, and also to include suggestions for other materials than you original to best suit your wishes (hygienic, lifetime, price, or price over lifetime, etc. etc...)

 

[DAquilina]

gerhardl,

Thank you for the advice.

 

[valvesarefun]

I have quite a bit of experience with these types of butterfly valves, although not in your particular application. My background is Oil & Gas valves, and we sell alot of butterfly valves with a nylon 11 coated disc. The coating, generally speaking, remains intact very well in clean water systems. However, no coatings will remain intact forever. Once the coating fails, the pieces/chips will have to travel somewhere downstream. Wether or not they will be of sufficient size or hardness to be detrimental to your other equipment, I cannot say.

Also important is the fact that once the coating is compromised you will have an exposed metal substrate. Most manufacturers that I am familiar with (including my company) use Dutile Iron as a substrate. Exposed ductile iron may, or may not, be a problem in your application. Its just a call you would have to make.

 

[DAquilina]

That is the big question, right now our spec only accepts bronze discs and though nylon coated discs may work well, at one point they are going to break down, chip and potentially damage our system.

Your comment follows this line of thinking.

Thanks,
Dave

 

[valvesarefun]

Dave,

Yes indeed. No coating can claim to be free from holidays, or to remain bonded forever.

What is the force driving you to consider other options besides the bronze disc?

-Vrf

 

[impeller1]

I'm assuming cost is a major factor to you? I'm familiar with butterfly valves which carry the nylon 11 coating. It works well in our seawater applications and protects the disc from corrosion. Is this for temporary use? Or long term? As mentioned above, the coatings do chip overtime as no coating will last forever. In my experience, the coatings we have lasted approximately 6 - 7 years whilst exposed constantly to seawater. However, the pressure wasn't very high - 20 psi max.

If you're concerned about chip fragments and it's for long term usage, I would recommend you keep to your bronze disc specification.