Why the Aquatrol 740 Series Is the Industry Standard
The Aquatrol 740 Series is a multi-purpose safety relief valve designed for air, gas, liquid, and steam service. It is ASME Section VIII (“UV”) certified, National Board (NB) registered, and available with CE and CRN certifications for international and Canadian applications. Aquatrol has manufactured safety and relief valves in the United States since 1947, and the 740 Series is their flagship product line. As an authorized Aquatrol distributor, we stock the full 740 Series with factory-direct pricing.
This guide covers everything an engineer or procurement professional needs to know to specify, size, and order the right 740 Series valve: configurations, pressure and temperature ratings, material options, sizing data, and ordering information.
Series Overview: 740, 741, 742, and 743
The “740 family” actually includes four related series that share the same fundamental design but differ in material construction. Understanding which series to specify is the first decision in the selection process.
| Series | Body Material | Internal Materials | Max Pressure (Air/Gas/Liquid) | Max Pressure (Steam) | Temperature Range |
|---|---|---|---|---|---|
| 740 | Bronze/Brass | SS nozzle, ring, disc, springs | 350 psig | 250 psig | -60°F to 406°F |
| 741 | Bronze/Brass | Full SS nozzle, ring, disc, springs | 1,500 psig | 300 psig | -60°F to 406°F |
| 742 | Carbon Steel | SS nozzle, ring, disc, springs | 1,500 psig | 300 psig | -60°F to 406°F |
| 743 | Stainless Steel | Full SS construction | 1,500 psig | 300 psig | -320°F to 425°F |
When to Use Each Series
- Series 740: The default choice for most applications. Air receivers, compressed gas systems, process tanks, and general industrial service up to 350 psig. Bronze/brass body is corrosion-resistant, cost-effective, and widely accepted across industries.
- Series 741: When you need higher pressure ratings (up to 1,500 psig) but still want a bronze/brass body. The upgraded stainless steel internals provide better corrosion resistance and longer service life.
- Series 742: Carbon steel body for applications requiring all-steel construction — often specified in petrochemical, oil and gas, or high-temperature environments where bronze is not acceptable. Steel-to-steel flanged connections.
- Series 743: 100% stainless steel for corrosive environments, food processing (sanitary applications with Tri-Clamp connections), pharmaceutical production, chemical processing, and cryogenic service down to -320°F.
Available Sizes and Connections
The 740 Series covers inlet sizes from 1/2″ through 3″ with multiple connection options:
| Connection Type | Format | Available On |
|---|---|---|
| NPT Male x Female (MxF) | Male inlet, Female outlet | All series (740, 741, 742, 743) |
| NPT Female x Female (FxF) | Female inlet and outlet | All series |
| BSPT Male x Female | British Standard Pipe Thread | All series |
| BSPP Male x Female | British Standard Pipe Parallel | 740 and 741 only |
| Lap Joint Flange | ANSI flanged connections | All series |
| Tri-Clamp | Sanitary connections | 743 (stainless steel) |
Standard inlet x outlet size combinations include: 1/2″ x 3/4″, 1/2″ x 1″, 3/4″ x 3/4″, 3/4″ x 1″, 1″ x 1″, 1″ x 1-1/4″, 1-1/4″ x 1-1/2″, 1-1/4″ x 2″, 1-1/2″ x 2″, 1-1/2″ x 2-1/2″, 2″ x 2-1/2″, 2″ x 3″, and 3″ x 4″.
Seat Material Selection
The seat (disc) material determines what media the valve can safely handle and at what temperatures. This is one of the most critical specification decisions.
| Seat Material | Service Types | Temperature Range | Key Properties |
|---|---|---|---|
| Metal (Stainless Steel) | Steam, Air, Gas, Liquid | -60°F to 406°F | Required for steam service. Highest temperature capability. Tightest seal at elevated temperatures. |
| Viton (FKM) | Air, Gas, Liquid (no steam) | -15°F to 400°F | Excellent chemical resistance. Better bubble-tight seal at lower pressures than metal. Standard for air/gas service. |
| PTFE | Air, Gas, Liquid (no steam) | -320°F to 450°F | Broadest chemical resistance. Required for cryogenic applications. FDA-compliant for food contact. |
| Buna-N | Air, Gas, Liquid (no steam) | -40°F to 250°F | General-purpose elastomer. Economical option for standard air/gas applications. |
Selection rule of thumb: If your application involves steam in any capacity, you must specify a metal seat. For everything else, Viton (FKM) is the standard choice for air/gas service, PTFE for chemical resistance or cryogenic temperatures, and Buna-N for basic air/gas applications where cost is the priority.
ASME Certifications and Compliance
The 740 Series carries the following certifications:
- ASME Section VIII “UV” — Certified for unfired pressure vessels. This covers the vast majority of industrial applications (air receivers, process tanks, heat exchangers, etc.)
- ASME Section XIII — The current section governing overpressure protection devices (previously covered under Sections I and VIII appendices)
- National Board (NB) — All capacities are independently flow-tested and registered with the National Board of Boiler and Pressure Vessel Inspectors
- CE Marking — Compliant with European Pressure Equipment Directive (PED) for export and international projects
- CRN — Canadian Registration Number for installation in Canadian jurisdictions
The Series 560, Aquatrol’s dedicated steam safety valve, also carries the ASME Section I “V” designation for power boiler applications. If your application requires a Section I stamp, specify the Series 560 instead of the 740.
How to Size a 740 Series Valve
Sizing a pressure relief valve requires calculating the minimum required orifice area based on your system’s maximum possible overpressure scenario. The process differs by service type:
For Air and Gas Service
- Determine the maximum flow rate your system can generate (in SCFM or lb/hr)
- Identify your required set pressure (at or below vessel MAWP per UG-134)
- Calculate the minimum required orifice area using API 520 or ASME Section VIII Appendix 11 methodology
- Select the 740 Series valve with the next larger standard orifice designation (D, E, F, G, H, or J) that provides sufficient capacity
For Liquid Service
- Determine the maximum liquid flow rate (in GPM)
- Account for the valve’s rated coefficient of discharge for liquid (Kd)
- Size per ASME Section VIII Appendix 11 for liquid service
- Verify that the selected valve’s NB-certified liquid capacity meets or exceeds the requirement
For Steam Service
- Determine the maximum steam generation rate (in lb/hr)
- Specify a metal seat — elastomer seats are not rated for steam
- Verify that the selected valve’s NB-certified steam capacity (in lb/hr) meets or exceeds the requirement
- For the 740 Series, steam service is limited to 250 psig. For higher pressures, use the 741 or 742 Series (300 psig steam)
If you need sizing assistance, contact our engineering team with your system parameters and we will provide a valve recommendation with supporting calculations.
Common Applications
- Air receivers and compressed air systems — The most common application. The 740 with Viton seat in 1/2″ through 2″ sizes covers the majority of shop air systems. See our Air Receiver Valve guide.
- Pressure vessels and process tanks — General industrial process equipment built to ASME Section VIII. See our Pressure Vessel Valve guide.
- Steam systems and boilers — The 740 with metal seat for Section VIII steam applications up to 250 psig. For Section I boilers, use the Series 560.
- Food and pharmaceutical processing — The 743 (stainless steel) with Tri-Clamp connections meets sanitary requirements for clean-in-place (CIP) systems.
- Cryogenic systems — The 740 or 743 with PTFE seat handles temperatures down to -320°F for LNG, liquid nitrogen, liquid oxygen, and other cryogenic fluids.
- Data center cooling — Chilled water and refrigerant systems in critical infrastructure. The 740 provides reliable overpressure protection for cooling loops.
Ordering Information
To order or request a quote for a 740 Series valve, you will need to specify:
- Series: 740, 741, 742, or 743
- Inlet x Outlet Size: e.g., 1″ x 1-1/4″
- Connection Type: NPT MxF, NPT FxF, BSPT, Flanged, or Tri-Clamp
- Seat Material: Metal, Viton (FKM), PTFE, or Buna-N
- Set Pressure: Specified in psig
- Service Type: Air/Gas, Liquid, Steam, or combination
- Cap Style: Closed (standard), Open Lever, or Packed Lever
Browse our full 740 Series inventory in our online store, use the Valve Finder to search by specification, or request a custom quote for non-standard configurations.
Frequently Asked Questions
What is the lead time for 740 Series valves?
Standard configurations typically ship from stock. Custom set pressures, non-standard materials, or special certifications may require additional lead time. Contact us for current availability on your specific configuration.
Are 740 Series valves field-repairable?
ASME-coded safety relief valves should only be repaired by facilities holding the appropriate National Board “VR” (Valve Repair) stamp. Field adjustments to set pressure on code-stamped valves are not permitted. For non-code applications where field adjustment is needed, consider the Aquatrol Series 69, which is designed for field adjustment.
Can the 740 handle back-pressure?
The standard 740 Series is a conventional (non-balanced) design. Superimposed constant back-pressure up to 10% of set pressure is generally acceptable. For applications with higher or variable back-pressure, contact our engineering team to discuss balanced bellows options.
What is Aquatrol’s warranty?
Aquatrol warrants their valves against defects in materials and workmanship. The company has maintained a near-zero return rate across their product line, reflecting the quality of their manufacturing and testing processes at their facility in Elburn, Illinois.
Ready to order? Browse 740 Series valves in our store, use the Valve Finder, or contact us for a quote. We typically respond within one business day.