Valve Selection criteria for Non Slam Check Valve (Nozzle type) 4

Suggest you buy Fluid Transients in Pipeline Systems by ARD Thorley or Pressure TRansients in Water Engineering by Paul Ellis where the subject is covered quite well.
The criteria you mentioned are wide of the mark

Non slam check valves are deployed after a dynamic analysis of the system shows that it is the best valve for the job NOT because it meets a list of criteria. Generally they are required where there are multiple pumps and one pump trips. Also where a gas accumulator is pseicified to reduce pressure transients.

A non slam valve such as the Noreva type has many benfits compared a swing check valve fitted with a counterweight and dampeners. For a start it is a very simple concept that doesnt require the maintenance of the dampener. With reduced resources in industry reliance on manitenance to ensure adampener functions is a questionnable practice.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

I agree with staniers post.

Please also note that in my opinion nozzle valves should be preferred above a swing check valve, including double eccentric BFL type swing check type, with dampeer for following reasons:

-easier and more simple maintenance and adjustment/dimensioning
-nozzle check valves can accept higher flow velocities at lower resistance than swing check valves and might be dimensioned down
-less resistance, energy loss (cheaper to operate when pumping.
-will accept a wider varity of flow-range than other types
-dimensioning and material/sealing properties to be selected/given by factory for best result for all types of checkvalves is necesssary. - All operation data to be given: minimum, normal and maximun flow, at what pressures (and delta Ps'), all fluid properties, line layout, softstart of pumps?, orientation when mounted, etc. etc.

Noreva is a good main brand in the nozzle-valves area with a varity of different selections. There are however competitors, Erhard for one, especially for water, but also a varity of other makes.

For very large sizes (above 800mm?????) nozzle-valves might not be available or best choice.

Govindarasu, I think you are well on your way to become a check valve expert. I work for Mokveld, one of the leading suppliers of nozzle or axial check valves. The information I will give to you is technical and based on information and operational feedback received from clients.

The term "non-slam" is one of the features of axial check valves. Some sophisticated swing check valve designs can be provided with this non-slam feature as well, however with certain side effects. In general the axial check valve is superior to swing and dual plate check valves but - like you already said - they are more expensive as well. The designation "non-slam", "nozzle" or "axial" check valve does not guarantee a good valve.

Some manufacturers like Goodwin Noreva, Crane Stockham, Mokveld and probably Cameron Entech have good understanding of the concept and gained dependable product data by means of dynamic and static studies with flow tests in reputable laboratories. Most other suppliers are copy cats that clearly have no idea about the design and product performance. A dual plate check valve from a good supplier may perform much better.

So where to use this special check valve? It is important to consider the application first. In general axial check valves are used for critical applications, which are those where:
[ul]
[li]Failure of the check valve will result in damage to critical and expensive equipment like compressors, pumps, valves and processing systems.[/li]
[li]Dynamic check valve performance is not sufficient to protect the same equipment[/li]
[li]Static check valve performance is not sufficient and compression or pumping energy will be wasted (high pressure loss)[/li]
[li]Reliability is essential to avoid system shut-down and economical damage.[/li]
[/ul]
Contrary to swing and wafer type check valves a good axial check valve is very stable in its operation and requires basically no maintenance. When you provide a good check valve supplier with proper flow, pressure, medium and deceleration data they will be able to present dynamic and static calculations.

One last note: there are two types of axial or nozzle check valves. Stockham and Mokveld have the central guided solid disc check valve for all valve sizes. For larger valve sizes Noreva and Entech prefer to supply the cheaper ring disc check valve. With two wide and flat sealing surfaces that ring disc valve has difficulties to grant tight shut-off. The ring disc is not pressure balanced (in closed position) and especially for compressor applications one should consider high cracking pressures that may affect operability of the system.

Dear Mr. Stanier, Mr Gerhardl & Mr Machiel,

Thank to all of you for providing such a informative reply.

Thanks

Govindarasu,
I can agree to 99% of the previous messages.
As I work for Noreva, I have to disagree to Machiel's last statement "cheaper ring disk check valve"
The ring disk design has basically been invented 1935 and is still the best combination of non-slam perfomance and low head losses.
Tight shut off requirements are over-estimated as check valves are considered to be safety valves for sudden backflow, not to be used as shut-off valves.
There shall always be an isolation valve downstream the check valve.

There is a rule of thumb for non-slam performance in liquid service which you may want to specifiy:
At any given decelaration of flow (dv/dt), the reverse flow (Vr) of any check valve shall be less than 0,2 m/s.
Well reputated manufacturers like Mokveld and Noreva shall be able to publish these figures based on independant dynamic behaviour testing.

I agree with Gustorf in that the ring type disc has advantages in larger sizes. One criteria for a non slam check valve is low mass of moving parts and the ring disc meets this criteria. In addition there has e been incidences of the shaft type axial check valve being compromised by debris in the flow stream or
corrosive products. The check valve is invariably open or closed for long periods. Where debris can get in the shaft bearing it can seize the assembly and the valve may not operate. This the valve may be stuck in the open or closed position. Worst still the disc may suddenly move quickly from one position to another as the stiction is overcome. This can provide a dangerous situation.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

Gustorf, thank you for your fair response. I think we can agree that the dynamic and static performances of the ring and disc nozzle check valves are quite comparable (standard design) ..... as are the prices .
The technical details, differences and reliability issues we better discuss at our clients meeting tables. I am somewhat surprised though about your rule of thumb with Vr to be less than 0,2 m/s irrespective of operating and design pressures (≈ 2 bar Joukovski pressure rise, water).

Stainier, you have put me in a somewhat difficult position here. I neither want to question the information you have nor speak negatively about ring type check valves in public. Can I contact you via blenrayaust@yahoo.co.uk?

Hi Machiel,

Better to see my website and find the more up to date email address as the one quoted was hijacked by spammers some time ago and is no longer used. I am actually in Australia.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King