Wafer Check Valve Failure Rates

[jsmfirepro]

I am working on a start-up project for which I need failure rate data for wafer check valves. Specifically failure to close. My application involves 10" wafer checks installed in a water system with a working pressure less than 175 psi. Please post experience and/or links to resources. Thanks in advance.

 

[gerhardl]

All experience will be related to all details of application and flow conditions, installation, pipeline layout, and of course all details of type, construction, accuracy and quality, including details on geometry, sealing and frequency of operation, and flow variation. No waterhammer or gulping presumed, as this is a sign of wrongly selected layout and dimensioning.

Failure by startup is more than 95% failure to pick right type by all criteria, wrongly mounted or adjusted, damaged products (wrongly produced or damaged, scratched sealings mostly).

All that said and 'in order' for the type you have selected, your failure rate could be 'almost zero'. If not so critical operation: keep one or two complete in reserve, recommended with mounted and adjusted extra equipment (limit switches, counterweights, damping devices etc, if any). The most exposed position will be likely to fail first, or by unfortunate circumstances one damaged or failing by startup, say guesstimate one in 10 to 100. Expected lifetime: guesstimate five to twentyfive years.

If critical operation: select non slam soft closing nozzle check valve instead. (There exists a range of constructions from your type, up to nozzle check that generally will perform better, but not implying that the choice you mention is not satisfactorily)

 

[LittleInch]

jsm,

I agree with gerhardl. Whilst I love using wafer checks, they are not the sturdiest of NRVs and should only be installed where they are used to prevent accidental back flow and utilise a spring that won't break or dissolve. The key word here is accidental, not purposeful or regular. NRVs are only ever a best efforts to prevent reverse flow and if you think they will actually be used on a regualr basis then you need something a lot better than a wafer check as gerhardl says. I've seen standard flapper type check valves nearly disintegrate when exposed to full flow / high pressure reverse flow, but that doesn't make them un reliable.

I doubt there is any reliable information and would question why you want it. What exactly are your trying to prove or disprove?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

There's probably a bigger chance of installing them backwards than breaking. They probably also have a bigger chance to not seal completely, rather than failing outright, due to commissioning gloves, rocks, sticks and welding sticks that didn't get cleaned out of the line.

Independent events are seldomly independent.

 

[jsmfirepro]

@Littleinch, et.al.

These wafer checks are install on the discharge side of three fire pumps supplying our sitewide fire protection systems. The pumps are rated at 2500 gpm @ 130 psi. The check valves are UL Listed / FM Approved for this application and rated for 175 psi working pressure. Jockey pumps maintain a grid pressure of ~125 psi and the wafer checks prevent water from backflowing through the pumps into the water tanks. These wafer checks have been tagged "single point of failure" because if they catastrophically fail, then it is assumed that the sitwide fire water distribution system would be incapacitated. I believe a catastrophic failure of one of these check valves is highly unlikely; however, the folks want to know HOW highly unlikely. If no failure rate data exists, then I'll have to stick with a qualitative description. I appreciate all your comments and input.

 

[LittleInch]

In that sort of critical location, the usual corrective action is to install a secondary, different type of NRV in line withe wafer check.

Big bro' is right - you have a much higher chance of wafer checks not seating after use, at least not drip tight, especially after a few years, whereas other types of check valve such as inline, flapper type etc have rubber type sealing surfaces which seal a lot better. You may find that the leakage rate after a while exceeds your jockey pump capacity and/ or it runs a lot more than anticipated....

I don't think you'll get much data on failure as you describe, but you also need to think about the operation of these units on cessation of flow from the main fire pumps as they could easily slam shut. Other types of NRV can have a dmaping mechanism to reduce this shock which I would recomend you seriously consider.

A lot of this should come put in a HAZOP, but it's better to do it before if you can.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[jsmfirepro]

I forgot to mention - the wafer checks are NIBCO Class 125 Iron Body Silent Check Valves with renewable seat and disc. They are rated at 200 psi, not 175. The seat is Buna-N bonded to bronze.