Excess Flow Valve (EFV) Fundamentals

1. Operating Principles

An excess flow valve (EFV) is a safety device installed in a natural gas service line that automatically restricts gas flow when the flow rate exceeds a predetermined threshold. The valve is designed to close rapidly in the event of a service line rupture, excavation damage, or other catastrophic failure that would cause an uncontrolled gas release. Once the excessive flow condition is resolved and upstream pressure is restored, the valve resets and reopens to resume normal gas delivery.

Function

Automatic shutoff

Closes when flow exceeds trip point, limiting gas release from a damaged or severed service line.

Type

Passive safety device

No external power, actuation, or operator intervention required. Operates purely on fluid dynamics.

Reset

Self-resetting

Valve reopens automatically when excessive flow ceases and normal upstream pressure is restored.

Normal operation

Full-bore flow

Causes minimal pressure drop during normal gas delivery. Does not restrict appliance operation.

How an EFV Works

The EFV mechanism relies on the differential pressure created by gas flowing past an internal closing element. During normal operation, the gas flow is well below the trip threshold and the closing element remains in the open position, held by spring force or gravity. The valve presents a nearly full-bore passage with minimal restriction.

When the service line is damaged and gas escapes at a high rate, the increased flow velocity creates a pressure differential across the closing element that overcomes the holding force. The element moves to the closed or nearly closed position. A small bypass passage remains open to allow a controlled bleed flow that enables the valve to sense when the break has been repaired and upstream pressure has been restored.

EFV Operating Principle: During normal flow (Q < Q_trip): Differential force across closure element < Spring/gravity holding force Valve remains OPEN, full-bore passage During excess flow (Q > Q_trip): Differential force exceeds holding force Closure element moves to CLOSED position Only bypass flow passes (3-10% of rated capacity) Reset condition: Flow drops below trip threshold (Q < Q_reset) Upstream pressure restores to near normal Closure element returns to OPEN position Where: Q_trip = Trip flow rate (SCFH) - flow at which valve closes Q_reset = Reset flow rate (typically 80-90% of Q_trip) Bypass = Small flow to allow pressure sensing (1-10 SCFH typical)

EFV Design Types

Design Type	Closing Mechanism	Advantages	Common Applications
Spring-loaded poppet	Poppet disc held open by calibrated spring; DP overcomes spring to close	Precise trip point, orientation-independent, consistent performance	PE service lines, all orientations
Gravity-assisted ball	Ball held in pocket by gravity; high flow lifts ball to seat	Simple, reliable, low cost, self-cleaning	Vertical or near-vertical installations
Magnetic latch	Magnets hold closure open; DP overcomes magnetic force	Adjustable trip point, fast response	Steel service lines, higher pressures
Weighted disc	Weighted disc balanced in flow stream; excess flow tilts to close	Simple construction, field-adjustable in some designs	Horizontal installations, copper tubing

Key Performance Parameters

Trip flow rate: The minimum flow rate at which the EFV will close. This is the primary sizing parameter and must exceed the maximum connected load demand with an adequate safety margin.
Bypass flow rate: The small flow that passes through the valve when it is in the closed (tripped) position. Bypass flow is essential for the valve to sense when conditions are restored. Typically 3 to 10 percent of the rated trip flow.
Reset pressure: The upstream-to-downstream pressure differential at which the valve reopens after tripping. The reset differential must be achievable under normal operating conditions.
Pressure drop (open position): The pressure loss across the valve during normal gas delivery. A properly sized EFV should cause less than 0.3 psig pressure drop at maximum connected load flow.
Response time: The time from onset of excess flow to full closure. Most EFVs close within 5 to 30 seconds, depending on flow rate above the trip threshold.

Design philosophy: An EFV is not a shutoff valve. It is a flow-limiting device that reduces gas release in the event of a catastrophic service line failure. The bypass flow means some gas will continue to escape, but the rate is reduced from potentially thousands of SCFH to single-digit SCFH, dramatically limiting the hazard zone and time to ignition.

2. Federal Mandate (49 CFR 192.383)

The Pipeline and Hazardous Materials Safety Administration (PHMSA) codified the requirement for excess flow valves in 49 CFR 192.383, which took effect on February 6, 2010. This regulation was enacted following decades of advocacy by safety organizations and in response to gas-related incidents caused by excavation damage to residential service lines. The rule mandates that gas distribution operators install EFVs on all new and replaced service lines serving single-family residences where the service line is compatible with commercially available EFVs.

Regulatory Timeline

Year	Event	Significance
1998	49 CFR 192.383 initial rule	Required operators to notify customers about EFV availability; installation upon request only
2008	Pipeline Safety Improvement Act	Congressional mandate to PHMSA to require EFV installation on new/replaced service lines
2010	Final rule effective Feb 6, 2010	Mandatory EFV installation on new/replaced single-family residential service lines
2016	PIPES Act of 2016	Expanded scope consideration; PHMSA studies on multi-family and commercial applicability

Scope of the Mandate

49 CFR 192.383 Requirements: WHO must comply: All gas distribution operators (LDCs and municipals) WHAT service lines: New service lines installed after February 6, 2010 Replaced service lines (full replacement, not repair) Service lines serving single-family residences (SFR) Including small multi-family buildings (≤ 4 units) in some interpretations WHERE installed: On the service line between the main and the meter set Typically near the main connection (curb valve location) Must be accessible for testing and maintenance WHEN required: At time of new installation At time of full service line replacement Upon customer request (any time, customer pays labor/materials) EXEMPTIONS (192.383(c)): Service line not compatible with commercially available EFV Operating conditions prevent proper EFV function EFV would interfere with necessary line pressure or flow Operator documents reason for exemption in records

Operator Obligations

Installation: Install EFV on all qualifying new or replaced service lines at no additional cost to the customer.
Notification: Inform all existing customers (without EFVs) of the availability and benefits of EFVs. Provide written notification at least once.
Customer request: Install EFV upon customer request on existing service lines. Operator may charge the customer for installation costs.
Record keeping: Document all EFV installations, exemptions (with reasons), and customer notifications.
Sizing: Select EFV that will not interfere with normal gas delivery to connected appliances while providing protection against excess flow.

Penalties for Non-Compliance

PHMSA can impose civil penalties for violations of 49 CFR 192, including failure to install required EFVs. As of the most recent enforcement guidance, maximum penalties per violation per day can exceed $200,000, with annual maximums exceeding $2 million per related series of violations. Beyond monetary penalties, operators face increased regulatory scrutiny, consent orders, and potential restrictions on operations.

Practical impact: Since 2010, millions of EFVs have been installed across the United States. Industry data from AGA and PHMSA annual reports indicates that EFVs have been effective in limiting gas releases from excavation damage, the most common cause of service line failures. The cost per installation is typically between $50 and $200, while the safety benefit is substantial.

3. Sizing Methodology

Proper EFV sizing is the most critical aspect of compliance. An undersized EFV will cause nuisance trips during normal appliance operation, leading to gas service interruptions. An oversized EFV will not close during a service line rupture, defeating its safety purpose. The sizing process must balance these competing requirements by selecting an EFV whose trip flow rate exceeds the maximum demand of all connected appliances while remaining below the uncontrolled flow capacity of the service line.

Sizing Procedure

EFV Sizing Steps: Step 1: Determine connected load Q_load = Sum of all appliance input ratings (BTU/hr) / Heating value (BTU/scf) Example: Furnace 100,000 + Water heater 40,000 + Range 65,000 + Dryer 35,000 Total = 240,000 BTU/hr Q_load = 240,000 / 1,020 = 235 SCFH Step 2: Apply diversity/demand factor (optional) For residential loads, assume simultaneous operation of all appliances Diversity factor = 1.0 (conservative, all appliances running) Q_demand = Q_load x 1.0 = 235 SCFH Step 3: Apply safety factor Safety factor = 1.4 to 2.0 (AGA recommends minimum 1.4) Q_required = Q_demand x 1.4 = 329 SCFH minimum trip flow Step 4: Select EFV from catalog Choose smallest EFV with trip flow ≥ Q_required Verify EFV is compatible with pipe size and material Example: Select 350 SCFH EFV for 3/4" PE service line Step 5: Verify against pipe capacity Calculate maximum flow capacity of service line EFV trip flow must be < pipe capacity (otherwise valve never trips) Q_trip < Q_pipe_capacity Step 6: Check pressure and temperature corrections Adjust trip flow for actual operating pressure and temperature Q_trip_actual = Q_trip_rated x Pressure_factor x Temperature_factor

Connected Load Calculation

The connected load is the sum of the maximum input ratings of all gas appliances connected to the service line. Common residential gas appliance ratings are shown below.

Appliance	Typical Input (BTU/hr)	Flow at 1020 BTU/scf (SCFH)
Furnace (forced air)	60,000 – 120,000	59 – 118
Boiler (hydronic)	75,000 – 200,000	74 – 196
Water heater (tank)	30,000 – 75,000	29 – 74
Tankless water heater	120,000 – 200,000	118 – 196
Gas range / oven	40,000 – 75,000	39 – 74
Gas dryer	20,000 – 35,000	20 – 34
Gas fireplace (vented)	20,000 – 60,000	20 – 59
Pool heater	150,000 – 400,000	147 – 392
Standby generator	60,000 – 300,000	59 – 294

Standard EFV Sizes

EFVs are manufactured in standard sizes corresponding to common service line diameters and flow capacities. The following table shows typical commercially available EFV sizes.

Pipe Size (NPS)	Available Trip Flows (SCFH)	Typical Pressure Rating
1/2"	93	Up to 60 psig
3/4"	213, 350	Up to 60 psig
1"	500, 750, 1000	Up to 60 psig
1-1/4"	1250, 1500	Up to 60 psig
1-1/2"	2000, 2500	Up to 60 psig
2"	3200, 4000, 5000	Up to 60 psig

Pressure and Temperature Corrections

Pressure Correction: EFV trip flows are typically rated at 2 psig. For higher operating pressures, trip flow increases: Q_actual = Q_rated x sqrt((P_operating + 14.7) / (2 + 14.7)) Example: 500 SCFH EFV at 60 psig operating pressure: Q_actual = 500 x sqrt((60 + 14.7) / (2 + 14.7)) Q_actual = 500 x sqrt(74.7 / 16.7) Q_actual = 500 x 2.115 = 1,058 SCFH Temperature Correction: Q_actual = Q_rated x sqrt(T_base / T_actual) Where T is in Rankine (T_R = T_F + 459.67) At base 60 deg F and actual 30 deg F: Q_actual = Q_rated x sqrt(519.67 / 489.67) = Q_rated x 1.030 Temperature effect is relatively small (about 3% per 30 deg F).

Pipe Flow Capacity Check

The EFV trip flow must be less than the maximum flow capacity of the service line. If the trip flow exceeds what the pipe can deliver, the EFV will never close because the flow will never reach the trip point. The pipe capacity depends on diameter, length, inlet pressure, and gas properties.

Weymouth Equation for Pipe Capacity (Medium Pressure): Q = 433.5 x (T_b / P_b) x sqrt((P1^2 - P2^2) x d^(16/3) / (SG x T x L x Z)) Where: Q = Flow rate (SCFH at standard conditions) T_b = Base temperature = 520 R (60 deg F) P_b = Base pressure = 14.73 psia P1 = Inlet pressure (psia) P2 = Outlet pressure (psia) d = Internal pipe diameter (inches) SG = Gas specific gravity (air = 1.0) T = Flowing temperature (Rankine) L = Pipe length (feet) Z = Compressibility factor (approximately 1.0 at distribution pressures) Example: 1" PE pipe (ID = 1.049"), 100 ft long, 60 psig, SG = 0.60: P1 = 74.7 psia, P2 = 74.2 psia (assume 0.5 psi drop) Q = 433.5 x (520/14.73) x sqrt((74.7^2 - 74.2^2) x 1.049^(16/3) / (0.60 x 520 x 100 x 1.0)) Q approximately 2,850 SCFH The EFV trip flow (e.g., 1,000 SCFH) is well below pipe capacity, so the valve will function correctly.

Sizing rule of thumb: For typical residential service lines (1/2" to 1" PE, 100 ft, 60 psig), the pipe capacity is several times the connected load. An EFV with a trip flow of 1.4 to 2.0 times the connected load flow will provide adequate protection without risk of nuisance trips. Always verify with actual calculations for non-standard installations.

4. Installation Requirements

Proper EFV installation is essential for reliable operation. The valve must be installed in the correct orientation, at an appropriate location on the service line, and using methods compatible with the pipe material. Industry standards from AGA, ASTM, and individual manufacturers provide detailed installation procedures.

Installation Location

Preferred location: At or near the connection to the gas main, upstream of the curb valve or at the tee/saddle connection. This location maximizes the length of protected service line.
Alternative location: Near the meter set assembly, downstream of the curb valve. Less common but acceptable when main connection access is limited.
Accessibility: The EFV must be accessible for testing and replacement. Avoid installation in locations that would require extensive excavation for maintenance.
Depth: Install at the same depth as the service line, typically 18 to 36 inches below grade depending on local requirements and frost line depth.

Installation by Pipe Material

Pipe Material	Connection Method	Special Considerations
Polyethylene (PE)	Butt fusion, electrofusion, or mechanical compression	EFV body is typically PE with internal mechanism. Butt fusion preferred for permanent joint. No thread sealant needed.
Steel	Threaded (NPT), welded, or compression fitting	Apply thread sealant (PTFE tape or pipe dope) on all threaded connections. Verify pressure rating of fittings matches service line MAOP.
Copper	Flare fitting or compression	Use brass or copper EFV body to prevent galvanic corrosion. Flare fittings must be properly made with correct angle.

Orientation Requirements

EFV Orientation: Spring-loaded EFVs: Can be installed in any orientation (horizontal, vertical, angled) Flow direction arrow MUST point toward customer (downstream) This is the most common type for PE service lines Gravity-assisted EFVs: Must be installed vertically or within 45 deg of vertical Closure element relies on gravity to assist closing action Will not function properly in horizontal orientation Magnetic EFVs: Orientation per manufacturer instructions Generally any orientation, but verify with specific model CRITICAL: Always install with flow arrow pointing toward the customer. Installing backwards will prevent normal gas delivery.

Installation Procedure (PE Butt Fusion)

Verify EFV model, size, and trip flow rate match the design specification.
Inspect the EFV for shipping damage, debris in the bore, and correct flow direction arrow.
Prepare pipe ends per butt fusion procedures (face, align, heat, join).
Allow fusion joints to cool completely before pressurizing (per manufacturer cooling schedule).
Perform soap test on all joints for leak detection.
Verify the EFV opens fully by gradually pressurizing the service line.
Record installation data: EFV model, serial number, trip flow, date, location, and installer.

Common Installation Mistakes

Backwards installation: Flow arrow pointing toward main instead of customer. Gas will not flow or EFV trips immediately.
Wrong size: EFV pipe size does not match service line, requiring reducers that create additional pressure drop.
Gravity EFV horizontal: Gravity-type EFV installed horizontally; closure element will not seat properly.
Debris in bore: Construction dirt, fusion shavings, or packing material left in valve bore; causes nuisance trips or prevents closure.
Excessive fusion bead: Internal fusion bead restricts flow and can prevent closure element from seating.
Missing documentation: Failure to record EFV installation in system records; creates compliance gap.

Quality assurance: After EFV installation, conduct a flow test at the meter set to verify the EFV does not interfere with normal gas delivery. Open all appliances simultaneously and confirm adequate pressure at the meter. If pressure drops below the minimum delivery requirement (typically 0.25 psig for low-pressure, 6" w.c.), the EFV may be undersized or improperly installed.

5. Testing & Maintenance

EFVs are passive devices with no regular maintenance requirements under normal conditions. However, periodic verification of EFV operability is recommended as part of a comprehensive gas distribution integrity management program. Testing confirms that the valve will close when needed and reset properly after the excess flow condition is resolved.

Testing Methods

Test Method	Procedure	When Used
Flow-induced trip test	Intentionally exceed trip flow rate by opening a bleed port downstream of EFV; verify valve closes and gas flow is restricted to bypass level	Post-installation verification, periodic integrity checks
Pressure decay test	Isolate service line from main, pressurize from downstream, monitor pressure decay rate; compare to expected bypass flow	Non-intrusive verification without excavation
Reset verification	After trip test, restore upstream pressure and verify valve reopens and normal flow resumes within expected time	Always perform after any trip test
Visual inspection	Excavate EFV location, inspect for corrosion, damage, or settlement; check orientation	When excavation occurs near EFV for other work

Testing Frequency

There is no federally mandated testing interval for EFVs under 49 CFR 192.383. However, industry best practices and some state commissions recommend the following:

Post-installation: Verify EFV opens fully and does not cause excessive pressure drop (required).
After service interruption: Verify EFV resets and gas flows normally after any outage event.
Periodic verification: Some operators test a statistical sample of EFVs every 5 to 10 years to verify fleet reliability.
After third-party damage: If the service line is damaged but not severed, verify the EFV did not nuisance-trip or sustain damage.

Maintenance Considerations

No routine maintenance: EFVs are designed for the life of the service line (typically 50+ years for PE) with no scheduled maintenance.
Replacement criteria: Replace EFV if it fails a trip test, causes repeated nuisance trips, or is damaged during excavation.
Corrosion protection: Steel EFVs installed on metallic service lines must be included in the cathodic protection system. PE EFVs with metallic internal components should be evaluated for compatibility.
Records: Maintain records of all EFV tests, replacements, and any nuisance trip events.

Field experience: Industry data from utility operators indicates that modern spring-loaded PE EFVs have very high reliability rates, with failure rates below 0.1 percent per year. The most common issue is nuisance tripping caused by improper sizing (EFV too small for the connected load) rather than mechanical failure of the valve itself.

6. Exemptions & Special Cases

While 49 CFR 192.383 broadly mandates EFV installation, the regulation recognizes that there are situations where an EFV is not operationally compatible with the service line or where installation would create other safety concerns. Section 192.383(c) provides exemption criteria that operators may apply on a case-by-case basis.

Recognized Exemptions

Exemption Category	Description	Documentation Required
Incompatible operating conditions	Operating pressure too low for EFV to function reliably; very low flow that does not reach any available EFV trip point	Engineering analysis showing no available EFV will operate correctly at site conditions
No commercially available EFV	Service line size or material has no compatible EFV from any manufacturer	Documentation of search for compatible EFV from multiple manufacturers
Adverse flow interference	EFV would cause nuisance trips during normal operation (connected load exceeds smallest available EFV trip flow)	Connected load calculation showing all available EFVs would nuisance-trip
Multi-customer service lines	Service line serves multiple customers through branch connections downstream of potential EFV location	Service line configuration diagram; consider EFV at each branch instead
Life safety equipment	Connected load includes gas-powered emergency generators or life-safety systems where interruption could create greater hazard	List of life-safety equipment, risk assessment comparing EFV benefit vs. interruption risk

Special Cases

Existing service lines: The federal mandate applies only to new and replaced service lines. Operators are not required to retrofit EFVs on existing service lines (but must offer installation upon customer request).
Commercial and industrial: 49 CFR 192.383 specifically applies to single-family residences. Commercial, industrial, and large multi-family service lines are not currently required to have EFVs, although some states have expanded the requirement.
Master meter systems: Mobile home parks, apartment complexes, and other master meter systems may have different requirements depending on whether the downstream piping is considered a "service line" under the regulation.
Farm taps: Service lines from farm tap connections on transmission pipelines may be exempt if the EFV would interfere with the regulator or measurement equipment.

State-Level Variations

Several states have enacted EFV requirements that exceed the federal minimum. These may include requirements for multi-family service lines, commercial service lines, or specific testing intervals. Always verify applicable state regulations in addition to 49 CFR 192.383. Notable states with expanded requirements include California, New York, Massachusetts, and Ohio.

Exemption best practice: Operators should narrowly apply exemptions and document the technical basis for each exemption in permanent records. PHMSA inspectors review exemption documentation during audits. If a commercially available EFV exists for the service line size and operating pressure, the operator should generally install it unless a specific technical reason prevents proper operation.

7. Failure Modes & Troubleshooting

Understanding EFV failure modes is essential for troubleshooting service interruptions and ensuring continued safety. EFV failures can be categorized as failure to close (the valve does not trip during excess flow), failure to open (nuisance trip or failure to reset), and degraded performance (partial closure, excessive bypass, or slow response).

Failure Mode Analysis

Failure Mode	Symptoms	Possible Causes	Corrective Actions
Failure to close	Gas continues at full rate during line break; no flow restriction observed	EFV oversized (trip flow exceeds pipe capacity); debris preventing closure element from seating; spring fatigue; backwards installation	Verify sizing; excavate and inspect; replace if damaged; correct orientation
Nuisance trip	Unexplained gas outages at customer meter; intermittent low pressure	EFV undersized (trip flow too close to demand); simultaneous appliance startup surge; pressure fluctuations on main	Recalculate connected load; upsize EFV; check for main pressure instability
Failure to reset	Gas does not resume after service line repair; customer remains out of gas	Bypass passage blocked; excessive reset pressure required; debris lodged in mechanism; upstream pressure insufficient	Verify main pressure adequate; allow extended time for reset; replace EFV if blocked
Excessive bypass flow	Continuous gas odor or leak indication when EFV is tripped; combustible gas readings at grade	Worn or corroded sealing surfaces; manufacturing defect; debris preventing full closure	Replace EFV; investigate if corrosive environment or contaminated gas supply
Slow response	Valve takes excessive time to close during excess flow; significant gas release before closure	Contamination or corrosion of mechanism; weak spring; flow rate only marginally above trip point	Replace EFV; consider smaller size if flow during break barely exceeds trip point

Troubleshooting Procedure

EFV Troubleshooting Flowchart: Customer reports no gas or low pressure: 1. Check meter set: Is meter operating? Regulator set correctly? YES -> Proceed to Step 2 NO -> Repair meter/regulator (not EFV issue) 2. Check main pressure: Is distribution main at normal pressure? YES -> Proceed to Step 3 NO -> Main pressure issue (not EFV issue) 3. Was there recent excavation near service line? YES -> Inspect for damage; EFV may have tripped correctly NO -> Proceed to Step 4 4. Did customer recently add new appliances or use many simultaneously? YES -> Possible nuisance trip; recalculate connected load NO -> Proceed to Step 5 5. Attempt to reset EFV: - Close customer meter valve - Wait 3-5 minutes for pressure equalization - Slowly open meter valve - If gas resumes: EFV has reset (investigate cause of trip) - If no gas: EFV may be stuck closed or bypass is blocked 6. If EFV will not reset: - Verify main-side pressure is adequate - Excavate and inspect EFV - Replace if damaged or blocked

Nuisance Trip Prevention

Nuisance trips are the most common operational concern with EFVs. They occur when the combined gas demand from all connected appliances momentarily exceeds the EFV trip flow rate. Prevention strategies include:

Adequate safety margin: Select EFV with trip flow at least 1.4 times the total connected load. A margin of 2.0 or greater virtually eliminates nuisance trips.
Accurate load calculation: Include all appliances, especially high-demand items like tankless water heaters and standby generators that may have been added after the original installation.
Startup surge consideration: Some appliances (especially older furnaces with standing pilots) create momentary flow surges during ignition. If nuisance trips occur during cold starts, consider the next larger EFV size.
Pressure correction: At higher operating pressures, the actual trip flow increases. Verify that the pressure-corrected trip flow still provides adequate margin.

EFV vs. Manual Shutoff Valves

An EFV is complementary to, not a replacement for, the manual curb valve or service shutoff valve. The curb valve remains the primary isolation device for planned maintenance and emergency shutoff. The EFV provides automatic protection against uncontrolled gas releases between planned shutoff events. Both devices should be present on every service line.

When to replace an EFV: Replace the EFV if it fails a trip test (does not close at rated flow), causes more than one nuisance trip per year, shows visible damage or corrosion, or if the connected load has increased such that the existing EFV is now undersized. Replacement is a straightforward operation that can be performed during a routine service line repair or meter set change.