Biogas and landfill gas stress valves chiefly through condensed moisture, hydrogen sulphide and siloxane deposits. Moisture and sulphide corrosion roughen sealing surfaces, while siloxanes and dust form deposits that make valves stiff or passing. Valves built with injection fittings can often be cleaned and protected in service, though severe corrosion or heavy build-up needs assessment before any treatment.
Knowledge ยท Valve types and applications
Biogas and landfill gas: wet, corrosive and variable
Wet, corrosive and variable gas attacks valves in ways clean, dry gas never does.
1. What the gas carries into the valve
Raw biogas is rarely clean or dry. It leaves digesters and landfill wells saturated with moisture, carrying hydrogen sulphide (H2S) and carbon dioxide. Landfill gas adds siloxanes, fine dust and biological growth, and its composition shifts hour by hour.
Each agent works on the valve differently. Condensed moisture washes lubricant from the ball and seat surfaces, then enables corrosion. Hydrogen sulphide, with moisture present, attacks the same surfaces as sulphide corrosion. Siloxanes and dust combine into sticky deposits that bind the trim.
The effects compound rather than add. A corroded seat holds deposit, deposit holds moisture, and the cycle repeats. Moisture condenses wherever the gas cools or drops pressure, often at the valve stations themselves. For the wider chemistry, see how wet, sour and carbon-dioxide-bearing gas behaves in valves.
2. How the damage shows up
Trouble usually shows as stiff operation, a seat that passes, or a stem that weeps. Each symptom suggests a direction, and none of them proves it. A valve that turns hard suggests deposits or early corrosion. A downstream pressure rise after closure suggests seat leakage.
Common causes include lubricant washed out by moisture, sulphide scale on sealing surfaces, siloxane and dust deposits, and trim damage from corrosion. The mix differs between digester plants and landfill sites, so screen first and test before acting.
Confirmation needs a test, not an impression. A seat-leak test under agreed conditions, such as pressure decay across the closed valve or double block and bleed monitoring, turns suspicion into evidence. Stem leaks are screened with a detector or soap film, then confirmed by a measured leak rate. On a methane-rich gas, that discipline also protects emissions reporting.
3. Where online treatment helps
Valves built with injection fittings are designed to be maintained in service. Not every valve on a biogas plant qualifies; some have no fittings, and some duties do not suit injection. Before recommending treatment, three gates apply:
- The injection fittings must exist and be in good condition.
- The valve design and this service must suit injection.
- Site rules and the permit-to-work must allow work on live gas.
Where OEM documentation exists, consult it for limits and warranty terms.
Through the fittings, a cleaner soaks and lifts deposits, a lubricant restores protection against moisture, and a sealant can restore seat tightness in suitable cases. Injection is controlled: measured amounts within equipment and fitting ratings, watching the pressure response, and stopping if pressure climbs abnormally. Badly neglected valves need longer soaking and more patience. The method is set out in our guide to valve sealant injection, and our clean, lubricate and seal service applies it in the field.
4. What injection cannot solve
Injection maintenance has honest limits on this duty. Corrosion that has removed metal from a seat or ball cannot be cleaned away; a sealant may reduce leakage for a time, but the right endpoint is a proper assessment, and often repair or replacement. Passing that continues after cleaning and a controlled sealant dose points to seat damage, not deposits.
A stem leak usually traces to packing that injection cannot reach; it needs packing adjustment or repair. A valve seized solid by corrosion is a workshop case, not an injection case.
None of this is a failure of the method; it is the boundary of it. Treating a valve that should be assessed wastes effort and can hide a defect. When severity is unclear, a condition survey is the evidence step we recommend first.
5. After upgrading, the gas changes
Upgrading to biomethane changes the enemy. The gas leaving an upgrading plant is dry and largely free of sulphide, so the corrosion drivers fall away. A new risk appears: dry gas can harden organic sealants and lubricants inside valves, and hardened compound can seize a trim that was healthy.
Compound choice therefore matters more, not less, after upgrading. Our valve lubricants are formulated in-house, and the right grade differs between raw and upgraded gas. Cycling also protects the trim, and common practice cycles valves at least twice a year to prevent seizing.
Where biomethane enters a city network, the network rules follow. See valve upkeep at city gas distribution scale for that regime. Records complete the work: log every treatment, the response, and the condition found.
Common questions
Biogas valve upkeep questions, answered directly
Why do biogas valves fail faster than natural gas valves?
Moisture and hydrogen sulphide corrode sealing surfaces, while siloxanes and dust form deposits that bind the trim. Natural gas is drier and sweeter, so it strips lubricant more slowly and corrodes far less. Failure patterns still vary between sites.
Can a leaking biogas valve be fixed without a shutdown?
Often, yes, when the valve has injection fittings in good condition and its design suits the service. A controlled dose of cleaner or sealant through the fittings restores many valves. A seat-leak test under agreed conditions confirms the result.
How often should biogas plant valves be serviced?
There is no universal interval. Common practice cycles valves at least twice a year to prevent seizing, and treats lubrication top-ups by condition rather than calendar. Sites with heavy siloxane load usually inspect more often.
Do siloxanes harm valves or only engines?
Engines bear the worst siloxane damage, because combustion converts them into hard silica deposits. In valves, siloxanes mostly act as part of sticky deposits with dust and moisture. Cleaners often lift such deposits while they are still soft.
Facing a stiff or passing biogas valve?
Send the valve details. An engineer replies within 24 hours.
Include the gas source, valve size and class, symptoms, and photos of the injection fittings.