Technical explainer
What Is a Monoflange Valve and How Does It Work?
A monoflange is a compact, flange-mounted valve assembly used at a process take-off. It can combine isolation and bleed functions close to the process connection, reducing separate threaded components in an instrument hook-up.
By SNG Services · Updated 1 Oct 2026
How a monoflange fits into an instrument hook-up
The process side mounts at the flange connection while the instrument or impulse connection leaves the compact body. Internal valve paths provide the isolation and bleed functions defined by the arrangement. The approved piping and instrument diagram governs how those paths are used.
Single isolation, block and bleed, and DBB
Monoflange is a physical product format, not one fixed valve schematic. Some arrangements provide one isolation path, some combine isolation with a bleed path, and some are configured for double block and bleed. Port diagrams should be compared rather than assuming the acronym defines every internal detail.
Why compact mounting is useful
Combining functions in one body can reduce the number of individual connections, shorten the hook-up and support a compact instrument layout. Access for operation, vent routing and maintenance still needs to be checked around the installed assembly.
Details that identify the required monoflange
Provide flange size, pressure class, facing, material, bore, valve arrangement, instrument connection, bleed connection and direction, service conditions, quantity and the applicable hook-up drawing or datasheet.
Next: prepare the RFQ
How to Specify a Monoflange Valve for an RFQ
Procurement guidance for monoflange valves, block and bleed monoflanges, DBB monoflanges and compact instrument isolation.
Read the buyer guideFrequently asked questions
Is every monoflange a double block and bleed valve?
No. Monoflanges are available with different valve arrangements. The flow schematic must be checked to confirm whether a specific assembly provides DBB.
Where is a monoflange installed?
It is commonly mounted at a flanged process take-off serving a pressure instrument, impulse connection, sampling point or similar compact hook-up.
Why is flange facing important in an enquiry?
The facing must match the mating process flange and project specification. Size and pressure class alone do not fully define the flange interface.