Industrial valve repair is the inspection, teardown, machining, re-seating, repacking, testing and documented return to service of plant valves, and Paul Industries repairs, tests, rebuilds, replaces and maintains gate, globe, ball, butterfly, check, control and pressure relief valves in all 50 states, with same-day emergency response. This page is written for the maintenance lead, reliability engineer or plant manager deciding on industrial valve repair for a leaking, sticking or overdue tag.
What is industrial valve repair?
Industrial valve repair restores a valve that leaks, sticks or has drifted from its set point to a measured condition, then proves that condition with a test before it goes back on the line. Evidence separates a repair from a swap: a body inspected, a seat measured, a stem checked and a result tied to a tag number. Valve service covers everything from a gland adjustment to new trim, and most plant valve services fall into one of three levels.
| Level | Typical work | Usually triggered by |
|---|---|---|
| In-service adjustment | Gland adjustment, lubrication, actuator and linkage checks, positioner calibration | Stem weep, sluggish stroke, a walkdown finding |
| Repair | Repack, replace seats and seals, lap sealing faces, replace a diaphragm, retest | Through-seat leakage, stem leak, failed test |
| Valve rebuild | Full teardown, clean to bare metal, NDE as needed, machine or weld-repair, new trim, reassemble, retest, repaint | Scheduled outage, repeat failure, a long-lead valve that must stay in service |
Valve reconditioning service: which documents apply
A valve reconditioning service sits at the rebuild level and has its own recommended practices: API RP 621 addresses metallic gate, globe and check valves, and API 6DR addresses pipeline valves. Naming the document in the purchase order sets acceptance criteria before anyone opens a bonnet. OSHA 29 CFR 1910.119(j) adds a legal layer, naming valves and relief devices in covered processes as equipment that must be inspected, tested and kept within acceptable limits.
Industrial valve repair by valve type
Industrial valve repair scope changes with geometry, because each design wears at different surfaces and fails in different ways.
| Type | What wears | Typical repair |
|---|---|---|
| Gate | Wedge and seat faces, stem threads, packing | Lap or machine seats and wedge, new stem or stem nut, repack |
| Globe | Plug and seat from throttling, stem, packing | Re-cut or replace seat, new plug, repack |
| Ball | Soft seats, ball surface, stem seals | New seats and seals, ball replaced if scored |
| Butterfly | Liner or seat, disc edge, shaft bushings | New liner or seat, bushings, disc alignment check |
| Check | Disc, hinge pin, seat; slam damage | Lap seat, replace disc and pin, confirm orientation |
| Control | Trim, packing, actuator diaphragm, positioner | New trim, repack, actuator rebuild, stroke test |
| Pressure relief | Seat, disc, spring, guide | Lap, replace parts, set on a bench, seat tightness test |
Throttling explains a lot of early gate and globe damage, since high velocity across a partly open seat erodes it quickly. On a gate used to control flow, the lasting fix is often a different valve style for the duty, sized with our valve Cv calculator. Sanitary diaphragm and clamp-end hardware has its own requirements, covered on our sanitary components and instrumentation page, and steam trap stations are covered on the steam traps page.
Ball seats, lined bodies and weld-end valves
A PTFE ball valve seat often sets the temperature limit of the assembly, since soft seats reach their limit well before a steel body. Published ratings for virgin PTFE seats run to about 400 degrees Fahrenheit and filled grades to about 500 degrees, subject to the manufacturer’s pressure-temperature chart. On a three-port body, pull the three way ball valve diagram before reassembly: an L-port or T-port ball installed a quarter turn out of position changes the flow path with no outward sign. A compact ball valve with a one-piece body often cannot be opened at all, which makes replacement the sensible repair.
A lined valve, with PTFE or PFA over the wetted surfaces, is inspected for liner cracks and blisters, since corrosive media can attack the metal behind a small defect. A butterfly, written as a BFV valve on many tag lists, can often return to duty in water or air service with a new liner. A weld valve, socket-weld or butt-weld, is cut out only when in-line work cannot reach the damage, and the repair of the joint then falls under the governing piping code. Surrounding spools and industrial valves and fittings belong in the same outage plan, and our process piping page covers that scope.
How a valve rebuild runs from teardown to return to service
A valve rebuild follows a fixed order, because each step produces a finding that the next step depends on. Skipping the as-received test or the measurements leaves an industrial valve repair with nothing to compare the finished work against.
| Step | What happens | What it records |
|---|---|---|
| 1. Receive and test | Confirm tag and history, then test before cleaning where the valve type allows it | Identity, as-found leak rate or set pressure |
| 2. Teardown and clean | Disassemble and clean to bare metal | Condition photographs, deposits found |
| 3. Inspect and scope | Measure critical dimensions; PT, MT, PMI or RT as the service demands; written scope and price | Dimensions, NDE results, approved scope |
| 4. Repair | Machine, weld-repair, lap, replace parts, repack | Parts list, weld records where welding is used |
| 5. Test | Shell, seat, stroke or set pressure test matched to the type | Test medium, pressure, duration, result |
| 6. Return | Tag, seal, protect ports, reinstall and leak-check | Final record tied to the tag |
On the isolation side of an industrial valve repair, the usual test reference is API 598, with a shell test at 1.5 times and a high-pressure closure test at 1.1 times the cold working pressure of the class. Control valves are tested to ANSI/FCI 70-2 instead. A repeat failure needs its root cause written into the next repair specification, or the rebuild only resets the clock.
How to replace valve packing
Valve packing replacement, the smallest industrial valve repair a plant performs, starts with isolating and bleeding the line and confirming zero energy on a gauge, with lockout and tagout on any actuator. The work then runs in this order:
- Set the valve partly open, remove the gland hardware and pull every old ring with a packing hook, counting them.
- Inspect the stem and box for scoring, corrosion and pitting, because a scored stem will chew through new rings.
- Cut new rings on a mandrel, not around the stem, and seat them one at a time with joints staggered 90 degrees.
- Tighten the gland evenly to the manufacturer’s torque, repressurize slowly and check for stem leakage.
Over-tightening is the classic mistake, because it adds friction that a handwheel or actuator has to fight on every stroke. Live loading, a spring set under the gland nuts, keeps load on the packing as it consolidates.
Valve packing materials: PTFE and flexible graphite
PTFE packing has low friction, which suits control valves, and is generally limited to about 450 to 500 degrees Fahrenheit because it extrudes at elevated temperature. Flexible graphite runs much hotter, with supplier ratings commonly quoted from about 850 up to 1,200 degrees Fahrenheit depending on grade and service, and it is the usual choice for steam and hot hydrocarbons. Combination sets pair PTFE with graphite to reduce friction compared with graphite alone, and low-emission sets are a sensible upgrade at a scheduled repack.
Control valve repair: actuators, positioners and trim
Control valve repair restores three things together: the trim that shapes flow, the actuator that delivers force, and the positioner that makes the stem go where the control system asks.
- Trim is the set of flow-controlling parts, usually plug, seat, cage and stem. Erosion, cavitation pitting and wire-drawing all show up here.
- The actuator is a spring-and-diaphragm, piston or electric unit. Its spring determines whether the valve fails open or fails closed on loss of air.
- The positioner compares a command, commonly 4 to 20 mA, with measured stem position and adjusts actuator air until they match.
| Symptom | Likely cause | Check or fix |
|---|---|---|
| Stem stays still, then jumps | Stiction, often packing too tight or a dragging guide | Compare command with position; correct packing and guiding |
| Response gap on reversal | Dead band, lost motion in linkage | Inspect linkage and connections, tighten or replace |
| Continuous hunting | Sticking valve, positioner fault, wet instrument air | Inspect first, check air quality, then recalibrate |
| Leaks when closed | Worn or eroded trim, weak seating force | Seat test, new trim, confirm the bench set |
| Noise and pitted trim | Cavitation or flashing | Review pressure drop and sizing; change trim or valve style |
Calibration cannot correct friction, backlash or a failing actuator, so physical faults come first and setup comes last. Controller retuning has the same limit: stiction is a hardware problem. Smart digital positioners add diagnostics that narrow the outage list for control valve repair services.
Control valve seat leakage classes after repair
ANSI/FCI 70-2 sets six control valve seat leakage classes, and a repaired unit should be tested against the class on its original specification.
| Class | Maximum seat leakage |
|---|---|
| I | No test required |
| II | 0.5 percent of rated capacity |
| III | 0.1 percent of rated capacity |
| IV | 0.01 percent of rated capacity |
| V | 0.0005 ml per minute of water, per inch of port diameter, per psi differential |
| VI | Bubbles per minute by port size, soft-seated valves |
Flow capacity comes up after any trim change. Valve Kv is the metric coefficient, defined in cubic meters per hour of water at a 1 bar pressure drop, and Cv equals 1.156 times Kv. Reduced trim changes both, so the replacement trim’s coefficient belongs on the record.
Hydraulic control valve repair
Hydraulic control valve repair restores the fit between spool and bore, because directional and proportional designs seal with clearance rather than a seat, and those clearances can be as tight as 0.0005 inch. Contaminated oil scores the spool, and each score becomes a leak path. Symptoms are sluggish response, drifting cylinders and spool leakage.
A hydraulic control valve rebuild strips scored spools, re-plates them with hard chrome and micro-grinds them back to tolerance, then cuts the oil grooves again. Bores or cartridges are honed where needed, sometimes with a spool built slightly oversize to match. New seals go in, and a test rig confirms the spool shifts in both directions under pressure. Hydraulic directional control valve repair on a press, a lift or plant machinery follows that sequence. Cleaning the oil at the same time keeps the repair from repeating.
How does a proportional valve work?
A proportional valve positions its spool in proportion to an electrical signal, using solenoid force working against a spring. Solenoid stroke follows input current, so spool position tracks the command. Closed-loop versions add an LVDT, which measures position so the electronics can compare it with the input and remove the error as flow, pressure and temperature change. Pilot-operated designs move the main spool with hydraulic pressure, often using pulse-width modulation at the pilot stage. A repair therefore checks the electronics and feedback as well as the spool.
Relief valve testing: what each test proves
Relief valve testing confirms that a pressure relieving device will open at its set pressure and reseat tightly, and no single test proves both. These devices are the last line of defense against overpressure, never pressure control devices.
| Test | Where | What it proves | Watch for |
|---|---|---|---|
| Lift lever check | In service, at 75 percent of set pressure or higher | Disc is free to lift | Says nothing about set pressure |
| Set pressure test on the unit | On the system, raised to full pressure | Actual opening pressure in place | Discharge energy and noise; needs a plan |
| Lift assist test | On-line, with an assist device | Set pressure without a full pop | Depends on the device and its calibration |
| Bench test | On a test stand after removal | Set pressure and seat tightness | Needs a planned outage or a spare |
ASME pressure vessel rules require a test lever on valves in steam, air and hot water above 140 degrees Fahrenheit. Pressure safety valve testing also starts with a look at the installation: no test gag left on, drains clear, a bellows bonnet vent open, seals intact and nameplate data matching the protected equipment.
Safety valve testing procedure on a bench
A bench safety valve testing procedure runs from as-found evidence to as-left proof. Record deposits and seal condition, then raise pressure slowly and note where it opens, before cleaning anything, since that result shows whether the service interval is right. After overhaul, the spring goes to the cold differential test pressure, which corrects for superimposed backpressure on a conventional valve and for operating temperature, so the nameplate set and bench number can differ.
The usual safety valve testing standard for seat tightness is API 527: hold 90 percent of set, or 5 psi below for sets of 50 psig or less, on air or nitrogen, and count bubbles from a 5/16 inch tube submerged 1/2 inch in water. The allowable rate depends on orifice and pressure, and soft seats should show none. For set pressure, ASME pressure vessel rules allow plus or minus 2 psi up to 70 psi and plus or minus 3 percent above that.
Pressure relief valve testing equipment means a stand with accurate gauges or transducers, a test volume sized to the orifice, and regulated air, nitrogen or water, and the gauges need calibration records of their own. For a tank vent, the pressure vacuum relief valve testing procedure checks each direction separately; API 2000 is the venting standard for tanks operating from full vacuum through 15 psig.
How often should pressure relief valves be tested?
Pressure relief valve test intervals depend on service and on the rule that applies, and jurisdictional rules take priority wherever they exist. The figures below are the National Board Inspection Code recommendations and API guidance.
| Service | Manual check | Pressure test or overhaul |
|---|---|---|
| Power boiler under 400 psi | Every six months | Annual pressure test |
| Power boiler over 400 psi | Per plant program | Every three years |
| High temperature hot water boiler | Per plant program | Annual pressure test |
| Low pressure steam and hot water heating boilers | Quarterly | Annually, before heating season |
| Vessels and piping, steam | Per plant program | Annually |
| Vessels and piping, air and clean dry gases | Per plant program | Every three years |
| Propane and refrigerant; valve above a rupture disk | Per plant program | Every five years |
| Other process service, API guidance | External visual with vessel inspection | Up to five years typical; up to ten in clean, non-fouling, non-corrosive service with documented history |
ASME pressure relief valve testing frequency is a frequent request, but the ASME code governs construction, so in-service intervals come from the sources above. ASME pressure relief valve testing requirements instead address certified capacity, test levers and set pressure tolerance. Safety valve testing frequency should tighten when as-received results drift or deposits appear. Under OSHA 1910.119(j), each test record must show the date, the person, the equipment identifier, a description of the test and the result. Refrigerant systems are covered further on our ammonia refrigeration page.
Steam boiler safety valve testing and repair
Steam boiler safety valve testing is done with the boiler on line at full pressure, or on a test stand after removal, and a valve found stuck shut means taking the system out of service. Boiler safety valve repair suits minor seat damage, which lapping and a retest can correct, while heavy corrosion usually means replacement. Isolation valves are not permitted between a boiler and its safety valve. Our boiler repair and steam piping pages cover the equipment and discharge lines around these valves.
Relief valve maintenance and the rules behind it
Relief valve maintenance is governed by a small group of named documents, and a good test record cites the one that applies. API RP 576 covers inspection, causes of failure, shop testing and records, and API 527 sets seat tightness testing. API 510 places responsibility for vessel inspection, including relief device intervals, on the owner-user. NBIC (NB-23) covers in-service inspection and repair, and NB-514 describes the National Board VR program for pressure relief valve repair.
Code repair of a stamped pressure relief valve falls under that VR program, which calls for a written quality system, witnessed repair of sample valves and independent testing of those samples for operation and capacity. A repair nameplate and matching seal then identify the organization, model, set pressure, capacity and date. NBIC treats a set pressure adjustment within twice the set tolerance as minor, and a larger change as a repair, and both require a qualified organization, defined as one accredited by the National Board.
What causes a pressure relief valve to fail?
Pressure relief valve failures fall into a handful of damage patterns described in API RP 576, each with its own corrective action.
| Cause | What it looks like | Corrective action |
|---|---|---|
| Corrosion | Pitted seat, thinned guide, cracked spring | Replace parts, review materials |
| Fouling or polymerization | Deposits in the nozzle, disc stuck to guide | Shorten interval, consider purge or rupture disk |
| Spring relaxation | Opens below set, loss of set after hot service | Replace spring, check temperature rating |
| Chatter | Hammered seat; inlet loss above about 3 percent of set, high backpressure or an oversized valve | Correct inlet piping or valve size |
A pneumatic safety valve on a compressed air receiver has a specific rule set: OSHA 29 CFR 1910.169 calls for capacity that holds pressure within 10 percent above the receiver’s maximum allowable working pressure, no valve of any type between receiver and safety valve, and testing at regular intervals. Our air compressor repair and pressure vessel fabrication pages cover the receivers.
In-place repair vs a valve repair shop
Industrial valve repair happens in place when the body is welded in or too large to move, and on a bench when the job needs machining, a test stand or a clean assembly area.
| Factor | In-place repair | Valve repair shop |
|---|---|---|
| Best fit | Welded-in or large bodies, light seat damage, repacking | Heavy seat damage, weld repair, control valve trim, relief valves |
| Method | Portable grinding and lapping machines mounted at the bonnet opening | Machine tools, lapping plates, test stands |
| Cost note | Field labor can run 50 to 100 percent above bench rates, per trade-press figures | Teardown and inspection billed even if the valve is scrapped |
Portable lapping handles light damage; resurfacing a seat takes a field machine with cutting and grinding tools, or a cut-out. At a shutdown or turnaround, valve repair services compress into a short window, so a tag list, pre-ordered parts and on-site spares decide whether the schedule holds.
Industrial valve repair vs replacement
Industrial valve repair is usually worth it when the repair quote stays under about 50 to 65 percent of a new valve, a range published as rules of thumb rather than a standard. Severe-service valves can justify more, with practitioners citing 75 to 80 percent, and critical special-order units are often repaired regardless because of lead time.
| Lean toward repair | Lean toward replacement |
|---|---|
| Alloy or stainless body, high new price | Small commodity unit where repair labor approaches the new price |
| Long lead time, or welded in and hard to remove | Cast-steel Class 150 below about NPS 12 or Class 300 below about NPS 10, by some refinery rules |
| Body sound, damage limited to trim or packing | Body or flange wall loss, cracking, obsolete parts |
Compare the life-cycle cost of an industrial valve repair and not just the purchase price, because lost production during a failure usually outweighs the difference between a remanufactured and a new unit. Paul Industries does both, repair and replacement.
How much does industrial valve repair cost?
Industrial valve repair cost is set by size, pressure class, material, trim condition, code and test requirements, and whether the work is in place or on a bench, so a figure only means something after teardown. Published sources give rules of thumb rather than a general price list. One trade-press worked example, explicitly hypothetical, used 40 control valves at $2,500 each, a $100,000 quote against $200,000 for new valves, then grew to about $150,000 after inspection findings added roughly 40 percent and a short delay added more.
That example makes the budgeting point: any industrial valve repair budget should carry an allowance for what teardown finds. Ask for separate pricing for teardown and inspection, then a fixed repair price once scope is known. Industrial valve repairs bundled into an outage are easier to price than one-off emergencies.
Industrial valve maintenance schedule
Industrial valve maintenance works best as a tag-based program ranked by consequence of failure, with tasks set by service and the manufacturer’s recommendations rather than a single calendar. Plant valves maintenance built that way cuts emergency industrial valve repair by putting effort on relief devices, critical control loops and the isolation points that must hold during outages.
| Task | Applies to | Trigger |
|---|---|---|
| Stroke rarely-used isolation units | Gate, ball, butterfly | Site procedure, before an outage |
| Check instrument air, diagnostics; repack and bench test as needed | Control valves | Scheduled review, hunting, or rising friction |
| Test or overhaul | All relief devices | Per the interval table above |
Valve maintenance services fit naturally inside a wider preventive maintenance or industrial maintenance scope, alongside the pumps, piping and rotating equipment around each tag. Paul writes and runs these programs as well as the repairs they generate.
Emergency valve repair: what speeds the response
Emergency valve repair moves fastest with answers on four items: service fluid and pressure, line isolation, a possible bypass, and any spare on hand. Paul Industries provides same-day emergency response in all 50 states; see emergency repair service for how to reach us.
Who performs industrial valve repair?
Paul Industries performs industrial valve repair, including control valve repair, relief valve testing, hydraulic valve rebuilds and valve replacement, for pharmaceutical, food and beverage, data center, oil and gas and general industrial plants. When comparing valve repair shops, these questions separate the bids:
- Which standard will the repair and test follow, and is it named on the quote?
- Will an as-received test be run and reported before cleaning?
- Does the record list as-found and as-left values, test medium and calibrated gauge identifiers?
- Will failed parts, photographs and a written root cause come back with the job?
The same questions apply to a valve repair service quoted for one tag and to a plant-wide contract. Valve service and repair priced per tag with no named test standard is the bid to question hardest.
Industrial valve sales & service: supply-only, design-build or complete installation
Supply and replacement come in three routes, supply-only, design-build and complete installation, and the plant’s needs beyond the hardware decide which fits. Paul sizes, supplies, installs and tests the replacement once an industrial valve repair shows the old one is finished.
Supply-only suits a like-for-like tag. Design-build suits a change of valve type or a new actuated package, and our turnkey process systems page shows that broader route. Complete installation covers removal, piping changes, welding, testing and startup. Industrial valve and automation work adds actuators, limit switches, solenoids and positioners to existing manual units, and the control signal gets integrated too, which our PLC programming page covers.
What Paul Industries does with plant valves
Paul Industries repairs, rebuilds, tests, supplies, installs, automates, replaces and maintains industrial valves in all 50 states. That includes industrial valve repair services for isolation, check, control, hydraulic and pressure relief valves, relief valve testing programs, in-place and bench work, and the piping, welding and startup around each one. To scope a job, send the tag list, nameplate photographs, service conditions and any past test records through our request a quote page.
Standards referenced: API RP 576 · API Standard 527 · API 510 · API RP 621 · API 6DR · API 598 · API Standard 2000 · NBIC NB-23 · NB-514 · ASME BPVC Section I · ASME BPVC Section VIII · ANSI/FCI 70-2 · OSHA 29 CFR 1910.119 · OSHA 29 CFR 1910.169
Frequently asked questions
What does valve service include on a full repair?
A complete job includes as-found testing where possible, teardown, cleaning, inspection, a written repair scope, machining or parts replacement, reassembly, a final test and a record tied to the tag. Depending on service, it can also include NDE, alloy verification and an updated nameplate.
What sets the turnaround time for industrial valve repair?
Turnaround depends on what teardown finds, how long parts take and how much machining or weld repair is involved. A repack can often be finished within a single isolation window, while a rebuild with new trim is set by parts availability, so long-lead tags are best planned around an outage.
Can industrial valve repair be done without removing the valve?
Many repairs can be done in line, including repacking, actuator work, and grinding or lapping gate and check valve seats with portable machines fitted at the bonnet opening. Line isolation and access are the main requirements, and a system-level test usually replaces a full bench test.
How much does a control valve cost to repair or replace?
Control valve pricing is driven by size, pressure class, body and trim alloy, actuator type, positioner and leakage class. Published repair-or-replace guidance compares the repair quote to the new price, and it is sensible to allow for inspection findings raising the first figure.
Who performs safety valve testing for industrial plants?
Paul Industries performs safety valve testing, relief valve overhaul and valve replacement across all 50 states, including bench tests and on-line tests with the unit in service. Plants can send a tag list with set pressures and service so the work can be planned by due date.
What is a safety valve testing machine?
A safety valve testing machine is a test bench that clamps the valve, applies controlled air, nitrogen or water, and shows on a calibrated gauge or transducer the pressure at which the valve opens. Records from it should carry the gauge's calibration identifier.
Can a pressure relief valve be repaired?
A pressure relief valve can be repaired when the body, nozzle and threads are sound and parts are available, using cleaned internals, lapped seats, new parts where needed, a bench set and a seat tightness test. Code repair of a stamped valve follows the National Board VR rules, which also set the repair nameplate. Small commodity valves are often replaced instead, since repair labor can approach the new price.
What decides that a pressure relief valve must be replaced?
Replace it when corrosion, a weakened spring, a bent spindle or a damaged nozzle cannot be economically corrected, when the valve is permanently sealed by design, or when a capacity change has made it the wrong size. Set pressure, capacity and code marking on the new unit have to match the protected equipment.
What is the difference between a pressure relief valve and a safety valve?
A safety valve opens with a rapid pop action to full lift and is used on steam, air and gas. A relief valve opens progressively with rising pressure and is typically used on liquids. A safety relief valve can serve either duty, and pressure relief valve is the umbrella term.
Where to install a pressure relief valve on a vessel or line?
Install it as close to the protected equipment as practical, with an inlet line that keeps pressure loss low, a full-size discharge with open drains, and no piping weight or strain carried by the valve. Discharge must be routed to a safe location away from people and walkways.
What is the purpose of a safety valve in a plant?
A safety valve protects people and equipment by relieving pressure when every other control has failed to hold it. Set pressure is chosen against the maximum allowable working pressure of the equipment, and the valve is expected to stay shut during normal operation.
Is a pressure relief valve adjustable in the field?
The spring setting is physically adjustable, but the adjustment is sealed for a reason. Under NBIC guidance, a change beyond twice the set tolerance counts as a repair, and every adjustment calls for a qualified organization, a new test record and a new seal.
What happens when a control valve goes bad?
A failing control valve shows up as a loop that will not settle: oscillation, slow response, an offset that returns, or process values that stay off target at full travel. Left alone it can cause off-spec product and upset nearby loops, so compare command and actual position early.
Is a butterfly valve a control valve?
A butterfly valve can serve as a control valve when fitted with an actuator and positioner and sized for the throttling range. Check the flow characteristic at the expected travel, since usable range narrows at small openings.
Can a ball valve control flow?
A ball valve can control flow if it uses a characterized or V-notch ball built for throttling. A standard full-port ball is an on-off device, and running it partly open erodes the seat quickly. Matching the ball style and actuator to the required range is what makes it work.
Valve packing vs seal: what is the difference?
Packing is compressible material loaded by a gland against a moving stem, and it can usually be adjusted while in service. A seal such as an O-ring or lip seal relies on its own shape and fit, so it generally has to be replaced when it starts to leak.
How do you tighten valve packing without damaging the stem?
Tighten the gland nuts evenly and in small steps with the valve at pressure, stopping as soon as the leak stops or slows to what the packing type allows. If the gland runs out of travel or the stem becomes stiff, the set is finished and should be replaced.
What is a test-only nameplate on a relief valve?
A test-only nameplate records that a valve was tested without being repaired, showing the test date and the responsible party. It gives traceability for the current setting if the valve was reset, and the seal on the valve should match that information.
What tests should a valve pass after industrial valve repair?
A repaired valve should be tested to confirm both pressure boundary and shutoff before reuse. The test type follows the valve: shell and seat tests for isolation valves, stroke and seat leakage for control valves, and set pressure and seat tightness for relief valves.
Can a hydraulic control valve be repaired if the spool is scored?
Scored spools can usually be repaired by stripping and re-plating with hard chrome, then grinding to restore clearance. If the bore is also damaged, it is honed and the spool is made slightly oversize to fit. Cleaning the oil and replacing filters afterward protects the new surfaces.
Related: Sanitary Components & Process Instrumentation · Process Piping · Steam Piping · Industrial Maintenance Services · Preventive Maintenance & Service Contracts · Plant Shutdowns & Turnarounds · Request a quote