What Should You Check Before Reopening a Soft-Seated Butterfly Valve That Has Remained Closed for a Long Time?

During shutdown, the pipeline may have been drained, solids may have settled, and the air supply or control settings may have changed. Before returning the valve to service, verify that the complete valve and piping system still meets the operating requirements.

Concentric butterfly valves with rubber seats are particularly vulnerable to two problems: compression set and adhesion between the rubber seat and the disc edge after prolonged contact.

This article focuses on butterfly valves installed in pipelines and kept closed for extended periods.

1. What Has Changed on Either Side of the Valve During Closure?

1.1 Changes in the Overall System

Before reopening the valve, review the operating records instead of immediately pressing the start button:

• Is the upstream side still pressurized, and has the downstream side been drained?
• Has maintenance on downstream equipment been completed, and is it ready to receive the process fluid?
• Does the pipeline contain residual cleaning chemicals, trapped gas, or crystallized material?
• Were any changes made to pumps, bypass piping, control logic, or actuator travel stops during shutdown?

The process fluid, temperature, upstream and downstream pressures, actuator model, historical torque or current readings, duration of closure, and whether the seat was replaced during the last service all determine the load and process consequences of the first opening. For piping that has undergone downstream maintenance, confirm that isolation has been released and all return-to-service conditions are satisfied. Do not “try opening it” to find out whether the system is ready.

1.2 Hidden Changes in the Butterfly Valve

Butterfly valves do not have the same trapped-liquid body cavity issue as ball valves, but the sealing line itself forms a narrow crevice. Once the valve is fully closed, fluid in that crevice becomes stagnant, oxygen is depleted, and deposits, salt crystals, and microorganisms accumulate along the disc edge. Rubber also becomes significantly stiffer at low temperatures. A valve closed in summer may require much higher breakaway torque when reopened on a cold winter morning than at room temperature.

The stem, pins, and keys are easily overlooked. Hardened packing, corrosion in the bushings, and hardened grease can raise operating torque well above the factory value. An actuator selected using the original clean-service torque may appear to have an adequate safety margin. After years of service, however, that margin may have been consumed by packing compression, bearing corrosion, and seat adhesion. On older valves, the actuator position pointer often differs from the actual disc angle. Causes include worm gear wear, loose pins, coupling slippage, or even an internally sheared disc pin while the handwheel continues to turn freely.

Failure mechanisms therefore accumulate in a butterfly valve that remains closed for a long time: adhesion increases breakaway torque, corrosion increases friction, and pipe settlement and flange stresses add further resistance, while actuator capability declines. A torque switch trip is more than an alarm; it signals that the available operating margin has been exhausted.

2. Check Differential Pressure, Not Just the Pressure Rating

Assume the same butterfly valve is in the following two conditions. All pressures are gauge pressures:

This hypothetical example illustrates differential pressure; it does not define the permissible conditions for any specific valve model. The upstream pressure is identical in both cases, but the differential pressure acting on the disc is significantly different.

Bray’s technical manual for resilient-seated butterfly valves identifies differential pressure as a factor affecting unseating torque. It also notes the effects of seat friction, disc edge condition, and interference after installation. Therefore, “PN16” alone cannot establish whether an actuator can reliably open the valve under the actual conditions.

If the system has a properly engineered pressure-equalizing bypass, use it according to the operating procedure. If no bypass is provided, do not loosen flanges, shaft seals, or other connections to relieve pressure.

3. Difficult Initial Unseating Does Not Mean the Entire Stroke Will Be Difficult

During the first movement after prolonged closure, pay particular attention to the disc’s initial rotation away from the sealing contact position. However, difficult initial movement is only a symptom; it does not automatically mean that the seat has aged.

Distinguish between the following symptoms during troubleshooting:

Do not use an extended handle, repeated jogging, or higher protection settings to force the valve past a sticking point.

4. Deposits Can Damage Sealing Surfaces as Well as Obstruct Movement

For raw water, circulating water, and fluids containing solids, review shutdown records for settling, scale formation, and drying of residual liquid. Deposits near the disc may obstruct rotation or enter the sealing contact area when the valve moves again.

Val-Matic’s butterfly valve maintenance manual lists internal deposits, debris, and actuator lubrication among the checks for difficult opening. Abnormal resistance therefore cannot be attributed solely to the seat material.

If the fluid has a strong tendency to crystallize, solidify, or cause abrasion, first establish a suitable cleaning procedure. Do not assume that high-velocity flow through a slightly open valve can safely flush away all deposits.

5. Actuator Movement Does Not Prove Sufficient Operating Capability

5.1 Pneumatic Butterfly Valves

For pneumatic butterfly valves, check the air pressure at the actuator inlet during movement. A normal pressure gauge reading while stationary does not rule out a significant pressure drop through the supply piping, filter, or solenoid valve when air is flowing.

5.2 Electric Butterfly Valves

For electric butterfly valves, review fault records, operating time, and available current or torque trends. Historical data provides a useful comparison, but motor current is not a direct measurement of valve shaft torque. It must be assessed together with voltage, transmission efficiency, and other relevant conditions.

If an overload trip occurs, first assess valve resistance and actuator condition. Before increasing output capability, verify the allowable loads of the shaft, coupling, and reduction gear. It is not enough to establish that the motor can still drive the valve.

In practical terms, do not conceal the underlying cause by fitting a larger actuator. Higher torque does not increase the strength of the disc pins or stem. The next seizure may cause a failure inside the valve.

6. Cross-Check Position Feedback Against the Actual Process Response

An “open” indication in the control room usually reflects the position of a feedback device. What that indication proves depends on whether the feedback is taken from the actuator, drive shaft, or another location.

When returning the valve to service, observe the following together:

• Is position feedback continuous and stable?
• Does it agree with mechanical indicators that can be observed safely?
• Do upstream and downstream pressures change as expected?
• Is the flow response consistent with the current pump and piping conditions?

If the valve indicates fully open but flow is abnormal, check the drive connections, feedback settings, other closed valves, and pipeline blockages. A single signal cannot identify the fault. Do not remove the actuator while the valve is pressurized to check the disc position.

7. Two Stages of Butterfly Valve Opening

7.1 The Unseating Region

The unseating region is the initial movement as the disc leaves the seat, generally about 0° to 15° for soft-seated valves. The main risk for soft-seated valves is concentrated in this stage. Begin with a small angular movement and observe whether torque rises smoothly or the valve suddenly jams. If it jams, back off and check for seat adhesion, seized bushings, or body distortion caused by piping stress. Repeated small movements can gradually release adhesion, but do not keep applying force at the jammed position. Fluoropolymer-lined and rubber-lined valves must not be forced: once the lining shifts, each subsequent opening or closing movement can worsen the damage.

7.2 The Rapid Flow-Change Region

The rapid flow-change region is the range where flow changes most rapidly with opening angle, generally about 30° to 70°. This is not the normal throttling position for the butterfly valve.

8. After Opening, Verify That the Valve Can Still Close Reliably

A successful first opening only verifies the opening action. Do not record “opens successfully” as “in good condition.” Opening only shows that the drive train has not failed; it does not prove that the sealing surfaces can still shut off flow. If the valve serves an isolation duty, verify the closed position and sealing performance under specified conditions during a suitable operating window.

Distinguish between:

• External leakage: leakage at the shaft, flanges, or body connections;
• Internal leakage: fluid continuing to pass through the sealing interface after the valve is closed.

A rise in downstream pressure after closure is not necessarily caused entirely by this valve. It may come from a bypass, other connected piping, or temperature changes. Confirm the test boundaries before assessing sealing performance.

9. A First-Opening Record Is More Useful Than “Operation Normal”

Keep the following records for critical isolation valves:

The first-operation record is particularly valuable. Smooth movement after several opening and closing cycles does not fully represent the initial response after a long shutdown. Human memory is unreliable, and the people closing and reopening the valve are often on different shifts. Without travel-stop records or records of fluid changes, treat the valve as potentially overclosed, exposed to a different fluid, or fitted with an inaccurate position indicator, rather than assuming the nameplate conditions still describe its state.

When purchasing butterfly valves that will remain on standby for long periods and must operate during a fault, tell the supplier the expected continuous closure duration, maximum opening differential pressure, tendency of the fluid to form deposits, and minimum available air supply conditions. Confirm the corresponding selection basis or verification method. Short-duration continuous cycle testing and the first opening after prolonged closure assess different conditions.

Set periodic operating-check intervals according to the manufacturer’s requirements, fluid characteristics, and the valve’s criticality, rather than applying one interval to every installation. Useful maintenance ensures that the valve’s response is documented and can be verified when it is next required to operate.