Internal Unions

Valco internal unions are precision-machined fluidic connectors designed to create true zero-dead-volume transitions between tubing segments in high-performance chromatography and analytical systems. These unions feature female threads with an integrated zero-volume fitting detail, while mating nuts use male (external) threads for secure, leak-resistant connections.

For optimal performance, select the union with a bore that matches your tubing ID. When connecting tubing with different internal diameters, always choose the union with a bore matching the smaller tube ID to minimize turbulence and maintain chromatographic efficiency.

Standard Valco internal unions are manufactured from 300 series stainless steel. Alternative materials including Hastelloy C, gold-plated stainless steel, and titanium are available for aggressive solvents, inert flow paths, and specialized operating conditions.

Bulkhead Internal Unions

Valco bulkhead internal unions are designed for mounting through instrument panels or brackets. The fitting body is precision undercut so it bites into the panel when the mounting nut is tightened—eliminating the need for a lock washer while providing a rigid, vibration-resistant installation for organized fluid routing.

TUBING OD BORE PART NUMBER
1/32"0.15 mmZU.5XC
1/32"0.25 mmZU.5
1/32"0.50 mmZU.5L
1/32"1/32"ZU.5T
1/16"0.15 mmZU1XC
1/16"0.25 mmZU1C
1/16"0.50 mmZU1M
1/16"0.75 mmZU1
1/16"1.0 mmZU1L
1/16"1/16"ZU1T
1/8"0.75 mmZU2
1/8"2.0 mmZU2L
1/8"1/8"ZU2T
Key Definitions â–¶
Internal Union
A zero-dead-volume fluidic connector with female threads used to join tubing segments while maintaining continuous internal flow paths.
Zero Dead Volume (ZDV)
A connection design that eliminates void spaces between fittings, minimizing sample dispersion and preserving chromatographic efficiency.
Tubing ID
The internal diameter of tubing. Internal unions should be selected with a bore that matches the tubing ID for optimal performance.
Bore Size
The internal passage diameter of the union. When joining different tubing sizes, the bore should match the smaller tubing ID to reduce turbulence.
Bulkhead Union
An internal union designed for panel or bracket mounting, featuring an undercut body that grips the panel when tightened—eliminating the need for a lock washer.
Material Options
Standard Valco internal unions are 300 series stainless steel, with optional Hastelloy C, gold-plated stainless, and titanium for aggressive or inert applications.
Frequently Asked Questions â–¶
What is a Valco internal union?
A Valco internal union is a zero-dead-volume connector with female threads designed to join tubing segments while maintaining a continuous internal flow path for optimal chromatographic performance.
How do I choose the correct bore size?
Select the union with a bore that matches your tubing ID. If connecting tubing with different internal diameters, always choose the bore that matches the smaller tube to minimize turbulence and sample dispersion.
What materials are available for Valco internal unions?
Standard internal unions are manufactured from 300 series stainless steel. Optional materials include Hastelloy C, gold-plated stainless steel, and titanium for aggressive solvents, inert flow paths, or specialized applications.
What is a bulkhead internal union?
Bulkhead internal unions are designed for mounting through instrument panels or brackets. The undercut fitting body bites into the panel when tightened, eliminating the need for a lock washer and providing a rigid, vibration-resistant installation.
Are Valco internal unions suitable for HPLC and UHPLC systems?
Yes. Valco internal unions are engineered for high-pressure chromatography environments and are commonly used in HPLC and UHPLC systems where zero-dead-volume connections are critical.