VX8 Low Pressure UHP Diaphragm Valve
Half-inch body with Cv 0.70 for branch lines and gas panel process legs where a 1/4 in valve would add too much pressure drop.
Built for ultra high purity specialty gas service, the VX8-LP belongs to the UHP Diaphragm Valves family covering isolation, switching and flow control.
VX8 Low Pressure UHP Diaphragm Valve overview
The VX8-LP is a high purity specialty gas valve specified with 1/2 ports, a flow coefficient of 0.70 and a maximum working pressure of 300 PSI. Half-inch body with Cv 0.70 for branch lines and gas panel process legs where a 1/4 in valve would add too much pressure drop. It is intended for the point in a high purity gas system where a clean, repeatable shut-off or switching function is needed without introducing a packed stem seal into the process stream.
A multi-layer metal diaphragm is clamped between the body and the bonnet, forming a hermetic barrier between the process gas and the actuator. There is no sliding stem seal, no packing and no lubricant in the wetted path, which keeps particle generation and trapped volume extremely low. A short, smooth flow path and low internal volume make purge cycles fast, which matters when a line changes between reactive gases. Available end connections are vcr face seal (male/female), butt weld, compression, so the same body can be used on face-sealed tool hook-ups, welded distribution headers or field-installed instrument lines.
Key features and design benefits
- 1/2 ports, Cv 0.70 — sized for 1/2 VCR diaphragm valve Cv 0.70 flow duty without excess dead volume
- 300 PSI maximum working pressure with a reinforced seat and helium-tested pressure envelope
- A multi-layer metal diaphragm is clamped between the body and the bonnet, forming a hermetic barrier between the process gas and the actuator.
- Electropolished wetted surfaces for fast dry-down and low moisture retention
- Manual or normally closed pneumatic actuation; pneumatic versions fail closed on loss of instrument air
- VCR, butt weld, compression or cylinder-standard end connections to match the installation
- Cleanroom assembly, double-bag packaging and per-valve leak records available
Technical specifications
| Port size | 1/2 |
|---|---|
| End connections | VCR face seal (male/female), butt weld, compression |
| Cv | 0.70 |
| Max working pressure | Manual: 300 PSI, Pneumatic: 150 PSI |
| Actuator supply | 60-90 PSI |
| Model code | VX8-LP |
| Product family | UHP Diaphragm Valves |
| Body material | 316L VIM/VAR stainless steel, low inclusion |
| Sealing element | Multi-layer 316L metal diaphragm, nickel alloy option for halides |
| Wetted surface finish | Electropolished, typical Ra 0.25 um (10 uin) or better |
| Leak testing | Helium mass spectrometer, inboard and across seat; typical 1 x 10^-9 mbar l/s |
| Operating temperature | Typical -10 C to +80 C manual, -10 C to +65 C pneumatic |
| Actuation | Manual handwheel or normally closed pneumatic, 60-90 PSI instrument air |
| Cleanliness | Cleaned, dried and assembled for ultra high purity gas service |
| Packaging | Cleanroom double-bag, sealed for installation |
| Documentation | Material certificate, helium leak record, certificate of conformance |
Values above describe the standard configuration of model VX8-LP. Final materials, seat, actuation, test limits and certification are confirmed on the order-specific datasheet issued with your quote.
Model comparison within the UHP Diaphragm Valves family
Select the body by flow demand rather than by port size alone. The table below compares the VX8-LP with its sibling models on the three parameters that drive a gas system design: port size, flow coefficient and maximum working pressure.
Construction and wetted materials
A multi-layer metal diaphragm is clamped between the body and the bonnet, forming a hermetic barrier between the process gas and the actuator. There is no sliding stem seal, no packing and no lubricant in the wetted path, which keeps particle generation and trapped volume extremely low. For the VX8-LP, the wetted path is machined from 316L VIM/VAR stainless steel with low inclusion and controlled sulfur content, then electropolished. A nickel-based diaphragm or seat alloy can be substituted where halide or hydride gases demand it.
| Component | Standard specification |
|---|---|
| Body | 316L VIM/VAR stainless steel bar stock |
| Wetted finish | Electropolished, typical Ra 0.25 um (10 uin) or better |
| Sealing element | Multi-layer 316L metal diaphragm, nickel alloy option for halides |
| Actuator | Manual handwheel or normally closed pneumatic piston, 60-90 PSI supply |
| Process connection | VCR face seal (male/female), butt weld, compression |
End connections and port options
The VX8-LP is normally ordered with 1/2 ports. Connection choice affects both cleanliness and maintainability: VCR face seals give a repeatable metal-to-metal seal for tool hook-up, orbital butt welds suit permanent high purity headers, and compression fittings are used where a line must be assembled in the field.
| Parameter | Available option |
|---|---|
| Standard port | 1/2 |
| End connections | VCR face seal (male/female), butt weld, compression |
| Seal standard | VCR face seal / orbital butt weld / compression / CGA or DISS for cylinder service |
| Actuation | Manual, or normally closed pneumatic with 60-90 PSI instrument air |
| Optional documentation | Material certificate, helium leak record, certificate of conformance |
Gas compatibility and typical applications
Model VX8-LP is selected for silane (SiH4), ammonia (NH3), hydrogen chloride (HCl), chlorine (Cl2), nitrogen trifluoride (NF3), tungsten hexafluoride (WF6) and high purity N2, Ar, He and H2. Always state concentration, temperature and any moisture or oxygen limit so the wetted alloy and seat can be confirmed before release.
- Semiconductor tool hook-up and gas cabinet isolation branches
- Valve manifold boxes, changeover panels and purge / vent legs
- High purity laboratory, analytical instrument and calibration gas lines
- Photovoltaic, MOCVD and hydrogen distribution systems
- Related application guides:
- Semiconductor Fab Gas Delivery
- Photovoltaic & Solar Cell Manufacturing
- Corrosive & Toxic Specialty Gases
Installation, purging and handling
Install the VX8-LP with the flow direction and port orientation shown on the approved drawing. Keep the protective caps in place until the joint is made, tighten face-seal fittings to the specified torque, and purge with dry inert gas before introducing process gas. Because the internal volume is low, a short cyclic purge is normally enough to reach the required moisture level.
- Handle with clean gloves in a controlled area; do not open the double bag until installation
- Use orbital welding or certified face-seal glands on high purity headers
- Purge with dry N2 or Ar and verify moisture / oxygen upstream before process gas
- Helium leak check the assembled joint, then the inboard and across-seat envelope
- Record the serial number, leak result and gas service in the system dossier
Ordering and configuration
Quote the model code and the options below. Where a gas is corrosive or pyrophoric, include the concentration so the diaphragm or seat alloy can be matched to the service.
| Ordering parameter | Your selection |
|---|---|
| Base model | VX8-LP — VX8 Low Pressure UHP Diaphragm Valve |
| Port size | 1/2 |
| End connection | VCR face seal (male/female), butt weld, compression |
| Actuation | Manual handwheel / normally closed pneumatic (60-90 PSI) |
| Wetted alloy | 316L VIM/VAR standard, nickel-based alloy by gas compatibility |
| Documentation | Material certificate, helium leak record, CoC (state if required) |
Ready to specify the VX8-LP?
Send the gas, pressure, flow and connection details — we will confirm the model, materials and lead time.
Related models and alternatives
Other valves in the UHP Diaphragm Valves family and adjacent groups that may suit a different Cv, pressure or port requirement.
VX4-LPVX4 Low Pressure UHP Diaphragm Valve
- Port size1/4, 3/8
- Max. pressure300 PSI
- Cv0.27
VX12-LPVX12 High Flow UHP Diaphragm Valve
- Port size3/4
- Max. pressure300 PSI
- Cv2.8
VX16-LPVX16 High Flow UHP Diaphragm Valve
- Port size1 in
- Max. pressure300 PSI
- Cv3.5
VX4H-HPVX4H High Pressure Diaphragm Valve
- Port size1/4
- Max. pressure4500 PSI
- Cv0.20
VX8H-HPVX8H High Pressure Diaphragm Valve
- Port size1/2
- Max. pressure3500 PSI
- Cv0.80
Frequently Asked Questions
What are the key specifications of the VX8-LP?
The VX8-LP is supplied with 1/2 ports, a maximum working pressure of 300 PSI and a Cv of 0.70. End connections are vcr face seal (male/female), butt weld, compression. The full specification table on this page lists materials, leak testing, actuation and cleanliness requirements.
Is the VX8-LP suitable for corrosive or toxic specialty gases?
It is used with silane (SiH4), ammonia (NH3), hydrogen chloride (HCl), chlorine (Cl2), nitrogen trifluoride (NF3), tungsten hexafluoride (WF6) and high purity N2, Ar, He and H2. Compatibility depends on the wetted alloy and the sealing element, so state the gas and concentration when requesting a quote and we will confirm the material selection.
How is the VX8-LP actuated and what is its safe state?
Standard configurations are a manual handwheel or a normally closed pneumatic actuator with 60-90 PSI instrument air. Pneumatic versions close on loss of air, which is the required safe state for most gas cabinet and tool hook-up isolation points.
How do I order the VX8-LP?
Quote model VX8-LP together with the gas list, operating pressure, required Cv, port size, end connection and actuation. Material certificates, per-valve helium leak records and a certificate of conformance can be supplied with the order.