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Frequently Asked Questions
How is one actually set?
By measurement, not by feel.
Test points sit either side of the orifice.
The differential across it is measured.
Converted to flow from the maker's chart.
And the valve adjusted to the design figure.
What is double regulating?
Closing without losing the setting.
The valve can be shut for isolation.
Then reopened to its commissioned position.
A stop remembers where that was.
It exists precisely for this.
What keeps it in such wide use?
It is simple, cheap and does not fail.
No cartridge, diaphragm or moving element.
Nothing to stick or drift.
At design condition it works indefinitely.
With no attention whatever.
When does the balance stop being right?
As soon as conditions leave the design.
Control valves throttling branches.
Partial occupancy, or varying load.
Pressures change and flows drift.
The valve cannot respond to any of it.
What happens after an alteration?
The system needs re-commissioning.
A site visit, with instruments.
To every valve, in sequence.
That rarely happens after small changes.
Which is why altered systems drift out.