Hollow and Solid Balls 2

[tigeralum]

Hi All,

Our supplier just informed us, they are going to use solid ball for a 2" floater and a hollow ball for a 3" floater.

will there be any difference in performance?

what is the reason they use hollow balls in some cases and solid in some?

Thanks in advance

 

[zdas04]

If the manufacturer got all his sums right, the only difference is the cost of metal vs. the cost of fabrication. If he's adequately stiffened the slot in the ball where the stem engages, and properly compensated for the differential pressure between the inside of the ball, the area upstream of the seat and the area downstream of the seat, the the two should work the same.

I guess an analogy that might fit is engineered wooden I-Beams. When these first came on the market, builders shunned them in favor of dimensional lumber. Over time the clear benefit of the I-beam became obvious and you rarely see a floor system in a home made from dimensional lumber today. My guess is that the hollow balls would be the same thing.

David

 

[tigeralum]

Thanks David.. nice post

 

[rneill]

I have not seen or heard of a hollow ball valve ball before. I would be a little concerned about this in some services. For example, we have historically accepted 316 SS balls in ball valves in sour service despite this material being quite limited by the current NACE MR0175/ISO 15156 document. I expect that the long history of successful service is directly related to the fact that the ball is a large solid chunk of metal and as such is in a very very low stress state.

If you were to manufacture a hollow ball, the assumption of a low stress state may no longer hold and we could start to see sour cracking where none had been seen before.

Myself, before I would accept a hollow ball, I'd want to ensure that the cost savings were being passed onto me and until there was some experience with them, I'd be a little wary of potentially unintended consequences as described above.

Also, I wonder about the fire safety of the hollow ball? I'd want to ensure that the valve was fully tested under the current API 607 fire test standard.

 

[zdas04]

rneil,
That is the kind of thing I meant when I said "If the manufacturer got all his sums right". There are probably a hundred important issues over and above what you or I could think of in a few minutes. If the manufacturer satisfied all the codes and is passing real cost savings on to the purchaser, then the valves will start to show up in parts houses. Some people will buy them and a history will start to build up. If there are no issues in the next 40-50 years then they'll "suddenly" be mainstream. Industries using ball valves are not exactly quick to adopt innovation.

David

 

[hsbcn]

I side with rneill and zdas04. I wouldn't go with it unless I'd absolutely have to, since it may also require you/end user to go back to that particular manufacturer for spares/maintenance. So the purchase value may be low, but the ownership value, stretched over the lifespan of the valve, may be quite high.

Heather Smith
My interests: Alloy valves, duplex valves, super duplex valves, 6Moly valves, inconel valves, incoloy valves, alloy 20 valves and titanium valves.

 

[gerhardl]

All parties are so far correct in my opinion, exept that the hollow ballvalve actually exists, and for cost reasons and weight reasons only: small awith exotic and/or highcost material or larger also with more common material with weight reasons in addition to cost.

If you commercially can buy a solid ball at equal, or slightly different pricelevel I would go for the solid ball.

If the pricelevel are lower for the hollow ball, or the difference totals to a larger sum, I would as stated above check references, certifications and qualifications for the manufacturer of hollow ball and ask for long-term references for the actual applications, to ensure troublefree performance and also analyze cost/lifetime consequences of using the hollow ball.

Some years ago I supplied a series of hollow ball constructed ball-valves for fairly large ballvalves and higher pressure classes with welded on exotic material overlay on the ball, for offshore use.

This total fabrication process is highly technically demanding, and a limited number of suppliers are able to supply certified top quality.

The end user was fully satisfied with price and performance and bought several times for similar processes over a number of years .

 

[rneill]

I thought I'd take a look at API 608 "Metal Ball Valves - Flanged, Threaded, and Welding End".

Clause 4.7 of this standard prohibits the use of hollow balls unless specifically agreed to by the purchaser.

I also found a reference elsewhere that said the use of hollow ball valves promotes turbulence and reduces CV factors although I find this strange. I have never seen a hollow ball though so I can't really comment one way or the other on that point.

 

[JimCasey]

A solid ball has a straight-through flow path thus presents minimal disruption to the flow. A hollow ball has continuous wall thickness so the flow experiences a diverging/converging cross section through the ball. Undoubtedly there is turbulence. Also if there is high differential pressure with the valve closed or the valve is closed too quickly and suffers water hammer, the hollow ball may become a hollow egg...no longer spherical.

That being said, the losses in ball valves are usually too low to notice, and it's a rarity that a hollow ball is damaged in service. A hollow ball is less expensive just becaouse there is less metal involved, and in larger sizes it will contribute to better seat life because its lighter weight reduces eccentric weight-related seat loading.

 

[gerhardl]

Hello Jim,

Seems that we perhaps differ in definition of 'hollow ball'.

Your definition seems to be directly sphereformed shell with a two holes 180 deg apart giving the full opening in and out.

I have seen this construction only as part of this 'shell' with a V-port opening to regulate the flow, a 'V-port ballvalve'

I have, on the other side, seen constructions for larger ballvalves where the througlet of the hollow ball is a pipe (full opening) welded into the spheric shell, giving same flow as for a solid ball.

I would, as always, appreciate your comments.

 

[rneill]

I had been assuming "hollow" balls were as described by gerhardl but in doing a quick google search, all I could come up with was hollow shells as described by JimCasey.

Both types are probably available somewhere ...

 

[itascot]

Hollow ball valves:
50-70% lighter than conventional solid balls.
20-40% decrease in seating/unseating torque.
Reduce weight, saving on shipping.
Reduced weight also help's reduce risk of damage to soft seats during assembly.
I had never heard of these before, apparently popular on smaller sizes (up to 2 1/2") and #300.
Attached sectional drawing of hollow ball.
Ciao,