Excess flow valves: automatic protection against line breaks or excessive flow
An excess flow valve is a mechanical safety component that automatically restricts or shuts off the gas flow as soon as the flow exceeds a set limit. An excess flow valve responds purely mechanically to the physical flow conditions in the line: without electricity, without a PLC and without human intervention. This article explains how excess flow valves work, when you need them and which ChemTec series suits your application.
⏱ approx. 7 minutes reading time
What is an excess flow valve?
An excess flow valve (EFV), also known as an overflow protection or safety shut-off valve, is a mechanical safety component that restricts or completely shuts off the flow as soon as the flow exceeds a set maximum level. The valve responds purely mechanically to the physical flow conditions in the line: no power, no signal and no external control are required. ChemTec offers the EFV and HPEFV series for applications ranging from small lab instruments to high-pressure process lines up to 6,000 PSIG.
The fundamental difference from a flow monitor is the response: a flow monitor detects a deviation and passes a signal to a PLC, which then takes action. An excess flow valve detects and responds independently in a single movement. That autonomous response makes the excess flow valve indispensable as the last line of safety in systems where a human or electronic response is too slow.
An EFV complements a flow monitor, it does not replace it
An excess flow valve and a flow monitor fulfil complementary roles. The flow monitor continuously monitors the process flow and gives an early alarm in the event of deviations, ideal for gradual leaks and process optimisation. The EFV switches automatically and mechanically in the event of a sudden, large flow excess such as a line break. In critical installations, both layers work together: monitoring for continuous control, the EFV as an autonomous emergency stop.
Operating principle: magnetic piston and pressure drop
All ChemTec EFV series work on the same principle: a magnetic piston in the valve body is held in its rest position by the attraction of an adjustable magnet screw. The incoming flow passes perpendicularly over the nose of the piston, creating a pressure differential across the piston. As long as the flow is normal, that pressure differential is smaller than the magnetic holding force.
1. Normal flow
The flow passes through the valve. The pressure differential across the piston is smaller than the magnetic holding force. The piston remains in its open rest position. No restriction of the flow.
2. Flow exceeds the setpoint
In the event of a sudden rise in flow due to a line break, fitting failure or regulator failure, the pressure differential across the piston increases sharply. At the moment this pressure differential exceeds the magnetic holding force, the piston shoots to its closed position on the seat at the outlet port.
3. Valve closes
The piston rests on the metal seat (controlled bleed version) or on an elastomer seal (positive shut-off version). The flow is restricted or stopped completely. The valve remains closed as long as the pressure differential across the piston is greater than the reset force.
4. Reset
After the cause has been remedied, the pressure across the piston equalises. The magnetic repulsion force of the fixed magnet in the valve body pushes the piston back to its open position. The valve resets automatically (controlled bleed) or requires a pressure equalisation procedure (positive shut-off).
The setpoint can be adjusted in the field by turning the magnet screw. The further the screw is turned into the valve body, the greater the magnetic attraction on the piston and the higher the actuation flow. Even a quarter turn has a measurable effect on the setpoint. ChemTec recommends a setpoint of three to four times the normal maximum flow rate to prevent unwanted activation due to start-up surges or normal flow fluctuations.
Setpoint recommendation: 3 to 4 times the normal maximum flow
A setpoint too close to the normal process flow leads to unwanted activation when the system starts up or during normal flow peaks. ChemTec recommends setting the setpoint at three to four times the normal maximum flow rate. Only when the flow is strictly constant may a setpoint of 10% above the normal flow be used.
Three reset options
ChemTec offers three reset variants for the EFV series, each with different behaviour after activation. The choice depends on the application and the desired degree of control after an emergency.
Controlled bleed (auto reset)
After activation, the piston rests on a metal seat that lets through a small controlled bleed flow. As soon as the source is shut off upstream or downstream, the bleed equalises the pressure automatically and the piston shoots back to the open position by magnetic repulsion. No manual action required. Standard version.
Manual reset (MRS)
On activation, the piston closes and the valve remains closed until you intervene yourself. Turning the lever on the valve body manually opens an integrated bypass, which equalises the pressure on both sides of the piston and returns the piston to its starting position. No external bypass line needed. Restarting is done deliberately and in a controlled manner, by an operator.
Positive shut-off (PSO)
An elastomer on the nose of the piston ensures bubble-tight shut-off on activation. To reset the valve, the pressure on both sides of the piston must be equalised: either by venting the upstream line or via an external bypass line with an on/off valve. Maximum sealing, deliberate restart mandatory.
EFV versus HPEFV: which series?
ChemTec offers two main series: the EFV series for standard to medium-high pressure and the HPEFV series for high pressure up to 6,000 PSIG. Both work on the same magnetic piston principle and are field-adjustable. The difference lies in the maximum working pressure range, the choice of materials and the specific applications.
EFV Series
Max. pressure: 1,500 PSIG (103 bar) brass / 3,000 PSIG (207 bar) 316 stainless steel
Material: Brass or 316 stainless steel; other materials on request
Seals: Viton® as standard; EPR, FFKM on request
Connections: ⅛" to ¾" FNPT (models 125 to 750)
Temperature: 0° to 220°F (−17° to 104°C)
Reset: Auto reset (bleed), MRS or positive shut-off
ES option: Reed switch contact (not on the 125 model)
Applications: Gas analysers, chemical processes, semiconductor, pharma, food & beverage, CNG distribution lines
HPEFV Series
Max. pressure: 6,000 PSIG (414 bar), 316 stainless steel only
Material: 316 stainless steel only; other materials on request
Seals: Viton® as standard; EPR, FFKM on request
Connections: ¼" to ¾" FNPT (models 250, 500, 750)
Temperature: 15° to 400°F (−26° to 204°C)
Factory preset: Mandatory for all HPEFV units; to be specified when ordering
ES option: Reed switch contact optional
Applications: CNG delivery, high-pressure process lines, hydraulic systems
HPEFV: factory preset mandatory
Unlike the EFV series, in which the setpoint can be set in the field, the HPEFV series requires a factory-set setpoint when ordering. When ordering, you specify the desired actuation flow (in SLPM), the gas type and the working pressure (PSIG). ChemTec sets the valve based on this information and delivers it ready for use. Subsequent adjustment is not possible without resetting by the factory.
Specifications and flow ranges
The table below provides an overview of all ChemTec excess flow valve models, with the adjustable flow range for air and water, the connection size and the maximum working pressure. The ranges are given for air at standard conditions (68°F, 14.7 PSIA).
| Model | Connection | Range air (SLPM) | Range water (LPM) | Max. pressure |
|---|---|---|---|---|
| EFV-125 | ⅛" FNPT | 0.5 to 155.7 | 0.015 to 4.5 | 1,500 / 3,000 PSIG |
| EFV-250 | ¼" FNPT | 4 to 1,132 | 0.1 to 15.1 | 1,500 / 3,000 PSIG |
| EFV-375 | ⅜" FNPT | 85 to 1,840 | 0.38 to 15.1 | 1,500 / 3,000 PSIG |
| EFV-500 | ½" FNPT | 142 to 2,123 | 1.9 to 37.8 | 1,500 / 3,000 PSIG |
| EFV-750 | ¾" FNPT | 425 to 3,681 | 3.8 to 75.7 | 1,500 / 3,000 PSIG |
| HPEFV-250 | ¼" FNPT | 4 to 1,132 | 0.1 to 15.1 | 6,000 PSIG |
| HPEFV-500 | ½" FNPT | 142 to 2,123 | 1.9 to 37.8 | 6,000 PSIG |
| HPEFV-750 | ¾" FNPT | 425 to 3,681 | 3.8 to 75.7 | 6,000 PSIG |
All flow ranges are given for air at 68°F (20°C) and 14.7 PSIA (1 bar atmospheric). A correction factor applies to other gases, other line pressures and other temperatures. Consult Inacom or ChemTec for the corrected actuation flow for your specific process conditions.
Applications
Excess flow valves are used in any situation in which a sudden, uncontrolled rise in flow causes immediate danger, damage or product loss. The most common applications are spread across a wide range of industries.
Gas analysers and laboratory equipment
Protects gas chromatographs, elemental analysers and other instruments in the event of fitting failure or hose rupture. Prevents expensive or hazardous analysis gas from flowing uncontrolled into the environment.
Chemical processes and semiconductor production
Protects process lines carrying toxic, flammable or corrosive gases. In the event of a line break, the EFV shuts off immediately, preventing exposure of personnel and damage to expensive process material.
CNG distribution and high-pressure plant lines
The HPEFV series up to 6,000 PSIG is specifically designed for CNG dispensing stations, high-pressure nitrogen and hydrogen installations and hydraulic systems where standard EFV pressure classes are insufficient.
Pharma, biotech and food & beverage
In regulated environments, the EFV provides mechanical protection that functions independently of electronics. Relevant for systems with inert gas, process air and steam.
Hydraulic systems
In the event of a hydraulic line break, the pressure can drop suddenly. The EFV responds immediately to the rise in flow and limits the loss of oil, preventing damage to actuators and hydraulic cylinders.
Toxic gas protection
In toxic gas release scenarios in which a leak of gases such as chlorine, ammonia or HF is immediately life-threatening, the EFV acts as the first mechanical barrier that stops the rise in flow immediately without waiting for an alarm system.
Selection guide: choosing the right EFV
| Situation | Recommended version |
|---|---|
| Working pressure up to 3,000 PSIG | EFV series 316 stainless steel |
| Working pressure up to 6,000 PSIG | HPEFV series, 316 stainless steel only, factory preset mandatory |
| Automatic reset after activation desired | EFV controlled bleed, auto reset as soon as the pressure equalises |
| Deliberate, manual restart required | EFV MRS, built-in bypass for a controlled restart |
| Bubble-tight shut-off required | EFV or HPEFV + PSO option, elastomer on the nose of the piston |
| Signal to PLC on activation | EFV + ES option (reed switch), not available on the EFV-125 model |
| Oxygen (O2) application | EFV or HPEFV + O2 option — oxygen-cleaned and fitted with oxygen-compatible materials |
| Aggressive media, FFKM seals required | EFV or HPEFV + KZ option (FFKM perfluoroelastomer) |
| ⅛" connection for small-bore installations | EFV-125 — smallest model, air 0.5 to 155.7 SLPM |
Setting the setpoint and installation
The EFV series is field-adjustable via the magnet screw on the outside of the valve body. Turning the screw changes the magnetic attraction on the piston and thus the actuation flow. ChemTec recommends calibrating the valve in the orientation in which it will also be installed, because gravity affects the piston position in vertical installation.
The flow ranges given in the calibration table are based on air at atmospheric conditions (68°F, 14.7 PSIA). A correction factor based on gas density and viscosity applies to other gases, other working pressures and other temperatures. For the HPEFV series, a factory preset is mandatory: when ordering, you specify the desired actuation flow in SLPM, the gas type and the working pressure in PSIG. ChemTec supplies the valve ready-set to those values.
Correction factor for other gases and pressures
The tables in the datasheets are valid for air at 68°F and 14.7 PSIA. For other gases (N2, H2, CO2, Ar) and higher line pressures, a correction factor applies that shifts the actuation flow. Inacom calculates the corrected actuation flow for your application based on your process parameters. Contact us for a customised calculation before selecting a model number.
ChemTec EFV and HPEFV at Inacom
Inacom supplies the complete ChemTec EFV product line for the Dutch market: the EFV series (⅛" to ¾"), the EFV MRS with built-in bypass, and the HPEFV series up to 6,000 PSIG. All options are available: controlled bleed, positive shut-off, reed switch contact, O2-cleaned and FFKM seals.
