Flow direction with balanced trim??

[HANYWEPCO]

Please I have the following items, appreciate if you can clarify to me:

1- For balanced trim , logically the flow should be up so that we can use smaller actuator to close the valve, but for some valves the flow is down while using balanced trim, Why?
2- What the criteria for flow up or flow down in the control valve?
3- What the meaning of HD in the plug type : 416SST HD ??

 

[Ehzin]

As a brief comment on item #1, my limited understanding is that it balances the "downstream" load on both the top and bottom of the assembly therefore balancing the majority of the vertical load that would cause difficult actuation for either opening or closing. Is installing it either way supposed to have a realistic impact on actuation?

For item #2, I believe you'll see flow down installations when used for certain anti-cavitation trim. It really depends on what you're trying to achieve by a certain flow path. Flow up, maintain a proper flow distribution over the disc for proper control while also possibly limiting the pressure that the packing is exposed to, especially if it isolates a low pressure from high pressure system. At least related to cavitation, certain flow down trim designs will limit the severity of cavitation in the first place while also using the flow distribution into the lower section of the valve to isolate the cavitation that will inevitably occur from mechanical damage on the valve itself.

There's likely many different reasons for flow up vs flow down. Think I've seen a video on how they control the location of cavitation collapse with the cavitation trims.

Thanks,
Ehzin

 

[gerhardl]

Hi HANYWEPCO!

1. (Wikipedias definition: a valve designed so that pressure-induced forces from the fluid being controlled oppose one another so that resistance to opening and closing the valve is negligible.)

Other factors in addition to flow direction will give the necessary operating force. The valve definition covers a multitude of different valves with a diversity of different detailed constructions. It is no general rule that the flow direction will give a large difference in operating force.

2. If you, by comparing all forces by flow up and down, find the difference large enough to influence the operator sizing, you might reconsider construction.

3. Probably HD=hardened.
(Grade 416 steel is a free-machining stainless steel with a machinability of 85%, highest of all stainless steels. With most of the free-machining stainless steels, the machinability can be improved by adding sulphur, which leads to the formation of manganese sulphide inclusions. Addition of sulphur also reduces the formability, weldability and corrosion resistance of 416 steels to below that of grade 410. Because of their high machinability and low cost, grade 416 steels are available in highly tempered, hardened or unhardened forms.)


Good Luck!

 

[HANYWEPCO]

Mr.Ehzin,
Can you please provide me the video of how they control the location of cavitation collapse with the cavitation trims.

 

[gerhardl]

Hi again!

Try

https://www.youtube.com/results?search_query=Cavitation+location+valve....

but not giving you the exact results you are looking for.

 

[Ehzin]

Sorry for just getting to this but they briefly mention it in Gerhardl's video around the 4:30 mark. Basically, that particular flow down trim attempts to isolate the bubble collapse from directly impacting the trim and other metal components. That particular part of the video shows it occurring within the center section as opposed to the lower portion of the valve like I had mentioned. I originally saw it in a still image and some brief comments in a Fisher catalog. I'll see if I can find some additional information tomorrow.

Thanks,
Ehzin