Repairing Hydraulic Servo Valves in Seismic Vibrator Trucks

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Not surprisingly, high-quality seismic data is mission-critical. Geophysical surveys can cost $50,000 or more per-square-mile depending on the territory, and multi-million dollar projects—sometimes billion dollar projects—are ultimately on the line. In short, there is no tolerance or margin for error in this industry.

Thumper trucks are intricate machines, however, powered by complex hydraulic and mechanical systems. To generate the massive force necessary for a controlled and effective sound blast, all equipment must be highly precise and high performing. For perspective, dynamite used to be the preferred method for this process!

Source: http://lingo.cast.uark.edu/LINGOPUBLIC/natgas/search/index.htm

When the base plate of the vibrating truck rapidly “thumps” the ground, the vibration puts acute stress on the mechanics driving the action. Hydraulic servo valves are a key example of this. By porting fluid and directing the hydraulic actuator to vibrate the base plate, servo valves are especially important components that are susceptible to wear and malfunction.

This video demonstrates how the vibrating trucks rapidly “thump” the ground.

High-intensity vibration exposes these high-performance valves, which are usually complex three-stage and four-way valves, to a variety of problems that can corrupt other parts and lead to equipment failure and downtime. Although these issues are difficult to diagnose in the field, servo valve failure is most often caused by the following:

1. Contamination: servo valves in vibrator trucks are exceptionally precise assemblies and the smallest particles can cause them to fail.

2. Internal part failure, especially:

1. Torque motor failures
2. Spools wearing out
3. AFSAs (a directional needle inside the servo valve) developing flat spots.

Source: http://hydraulicspneumatics.com/other-components/hydraulics-delivers-good-vibrations

Unfortunately, pinpointing the faulty servo valve component is only half the battle.

Once the defective or broken part is identified, most geophysical exploration companies rely on the component’s OEM to restore equipment to working order. This may mean replacing out-of-warranty defective parts with brand new, sometimes more expensive parts. The other option is to find a qualified independent service provider (ISP) that can identify the problem and restore or improve servo valve performance.

A larger ISP can offer surplus parts and emergency repair services to help limit downtime and reduce costs, which could help save 70% versus the cost of buying a replacement servo valve.

The ISP’s servo valve lab operations should always be set in a temperature-controlled, clean room environment. When a defective valve is shipped out and repair shop engineers have determined the full extent of its damage, the following repair steps should be executed:

1. Test servo valves on run-in test stands

1. Check performance to OEM specifications
2. Determine repair requirements

2. Analyze fluids running through the customer’s process

1. Recommend fluid improvements
2. Suggest maintenance requirements

3. Disassemble valve

4. Clean all parts ultrasonically in a heated vapor degreaser system

5. Replace all broken, worn and missing parts

6. Reassemble the valves using new fluoroelastomer seals

7. Test valves on a dedicated test stand capable of low- and high-flow testing

When the repair process is complete, the remanufactured, like-new condition servo valve should always meet the same industry specifications for performance as new valves.

Ron Fukui is director of engineering and technology for PSI Repair Services (www.psi-repair.com). He develops repair, test and reverse engineering strategies and manages the design team for new products. Reach him at r.fukui@psi-corp.com.