Why a new valve may not fit an older Solar Turbines package

A current-generation valve for a Solar Turbines package is not always a direct replacement for the valve fitted on an older unit. The new valve may need a different control signal, power supply, software, mounting or piping, and it may behave differently during start-up. On a package that has run for 20 or 30 years, those differences can turn a valve swap into a controls modification, and on units with a single fuel shutoff valve the change also touches the emergency shutdown system.

Many Saturn, Centaur, Taurus and Mars packages in Western Canada were built decades ago and are still in service on gas compression and power generation. When a fuel valve, shutoff valve or bleed valve fails, the part listed in the original parts book is often superseded by a newer design.

Why a newer valve may not fit an older package

1. A different control signal

Older fuel control valves were often driven by an analog signal from a driver card in the control panel. Newer valves can use a different signal range, an integrated electronic driver or digital communication. The existing panel may not be able to drive the new valve or read its feedback without new hardware.

2. Control system software and settings

The fuel schedule for light-off, acceleration and load changes was tuned to the original valve. A valve with a different flow characteristic, stroke or response time can cause failed starts, hot starts or unstable speed control unless the control settings are changed, and older control systems may not support the new valve at all.

3. Power supply

A newer valve may need a different supply voltage or more power than the existing circuit provides.

4. Mechanical fit

Flange size and rating, face-to-face length, connection type, weight and overall size can differ. In a crowded enclosure, a larger valve body or actuator may need new brackets or piping changes.

5. Hazardous area certification

The valve, actuator and wiring must carry certification accepted for the location, in Canada usually CSA. A valve certified for another market may not be acceptable on site.

6. Documentation and approvals

A different valve changes drawings, wiring diagrams and possibly the safety shutdown logic. Most operators will need a management of change review and re-commissioning before the unit goes back into service.

The fuel shutoff arrangement matters more than the valve

Many older gas-fuelled packages have one dedicated gas fuel shutoff valve, with the main fuel metering valve acting as the second shutoff device. Current packages are built differently: two independent shutoff valves, both separate from the metering valve, which is what control systems certified to the functional safety standard IEC 61508 expect.

This has three practical consequences when you replace a valve on an older unit:

• The metering valve is part of your shutdown system. On a single-shutoff package, a replacement metering valve must close reliably on its own spring when the run command is removed. An older valve whose internal electronics have been exposed to moisture or contamination can stay open after a close command, and the remaining shutoff valve is then the only protection.
• A control system upgrade can force a fuel system change. Moving an older package to a current-generation turbine control system may require either a dual shutoff valve assembly, or at minimum a current-generation metering valve plus wiring that drops the valve’s run command on any emergency shutdown.
• Space decides the route. A dual shutoff assembly is the preferred upgrade, but it may not fit in the existing enclosure or piping. In that case the minimum changes above are the alternative, and they still need engineering, parts and an outage.

These upgrades are usually at the owner’s cost, and the newer valves are often not stock items, so order well before the planned outage.

Options when the original valve is no longer available

An upgrade is often the right long-term answer, but it should be planned as a small project with the controls changes, not bought as a spare part.

What to send before you order

• Package serial number and turbine model (nameplate photos of the package and the valve)
• The valve part number and the superseding number, if you have one
• Control system type and version, and the wiring diagram for the valve
• Fuel gas pressure, temperature and composition
• Photos of the valve installed, showing connections and space around it
• Hazardous area classification at the valve

Send the valve and package nameplate photos on the quote form. We will tell you whether a repair, an equivalent or an upgrade fits your unit. See also gas turbine replacement parts.

CHR is an independent supplier and is not affiliated with or an authorized dealer of Solar Turbines Incorporated. Solar Turbines, Saturn, Centaur, Taurus and Mars are trademarks of their owner and are used here only to identify equipment.

Frequently asked questions

Is the superseding part number always a direct replacement?

No. A superseding part can be the recommended replacement for new or upgraded packages and still need changes on an older one. Check the signal, power, software and mounting before ordering.

Does my older package need two fuel shutoff valves?

Two independent shutoff valves, separate from the metering valve, is the current standard and the recommended upgrade. A package with one shutoff valve can usually stay in service if the metering valve and its shutdown wiring meet the minimum requirements, but an upgrade of the turbine control system is often the point where the change becomes necessary.

Can the old valve be repaired instead?

Often yes, if the body and actuator are sound and wear parts are available. Repair keeps the existing control settings and avoids a controls change.

Who should engineer an upgrade?

Someone who knows both the turbine package and your site’s controls and safety systems. CHR can review the change, prepare the documents for your management of change and supply the parts.