Begin with required driven-machine speeds
Obtain the normal and limiting shaft speeds required by the driven equipment designer. Distinguish useful operating targets from occasional transitions or maintenance conditions. State the available prime-mover speed range and any restrictions on sustained operation. A list of ratio numbers cannot establish whether the installed drive covers the required work. Require the bid to connect the proposed ratios with actual input and output conditions rather than treating the number of gears as a measure of suitability.
State the ratio convention and shaft references
Ask the supplier to define how each ratio is expressed and to identify the corresponding input and output shafts on a drawing. Include direction of rotation using an agreed viewing reference. A familiar ratio notation can still be misunderstood when the drive includes additional stages, reversals or auxiliary paths. Keep the convention beside the speed schedule so purchasing, engineering and inspection use the same definition when reviewing calculations and test results.
Review allowable load in every proposed ratio
Require the supported torque and power limits for the actual gear selections and speed range. A single maximum from one path should not be applied automatically to every gear. Ask the supplier to identify mechanical, lubrication or other restrictions that narrow an operating combination. The useful comparison is the set of supported work points, not the apparent range obtained by multiplying unrestricted catalogue extremes. Resolve any uncovered duty before accepting the configuration.
Separate ratio coverage from shifting capability
Identify whether the work requires stopping, unloading or another approved condition before selecting a different gear. Ask the supplier to state the permitted selection and engagement envelope for the offered mechanism. Multiple ratios do not establish synchronized or under-load shifting. The control and process teams should assess how the permitted transitions fit the rig operation, without assuming an operator can change gears whenever the required shaft speed changes.
Make the schedule part of acceptance
Record the agreed ratios, shaft identities, direction and corresponding measured-speed checks in the inspection plan. Identify test conditions and limits that apply to a no-load demonstration. If the final design changes tooth combinations or another drive stage, require an updated schedule and impact review. The handover information should allow the operating team to identify usable gear selections and restrictions without deriving them from an incomplete commercial brochure.
Check the gaps between operating choices
Ask whether the proposed prime-mover range and discrete gearbox ratios leave any required driven speed unsupported. A broad minimum-to-maximum output range can hide such gaps. Evaluate the selected work points with the actual drive controls and approved operating limits, not an assumed continuously variable transmission. If the proposal includes another speed-control component, list it in the supply and acceptance scope. This keeps the comparison focused on usable equipment performance rather than the size of the advertised ratio range.
Put these items side by side in the bid review
| Purchase item | Question to resolve | Evidence to request |
|---|---|---|
| Coverage | Which output tasks are supported? | Input-to-output speed matrix |
| Limits | Does each gear support the load? | Ratio-specific duty limits |
| Transitions | What conditions permit gear changes? | Approved selection envelope |
Suggested wording for the quotation request
Provide the complete ratio and shaft-speed schedule for the attached driven-machine cases. Define ratio convention, rotation reference, allowable load by gear and any gaps in coverage. State permitted gear-selection conditions and the proposed verification checks for the supplied configuration.
Assess each option within the complete gearbox drive train: prime mover, transmission, couplings, driven equipment, mounting and supporting oil system. Preserve the accepted load schedule and interface drawings when comparing suppliers or approving changes. A component rating should not be treated as proof of the complete installed arrangement. Obtain configuration-specific documents from the responsible designers, and retain the agreed exclusions and verification records with the equipment order. Installation, shifting, testing and maintenance must follow approved equipment instructions and site procedures rather than a procurement comparison.
For the wider equipment scope, consult the Oilfield Gearbox Ratio: Speed, Torque and Pump Drive. Use the RFQ checklist to collect the supporting documents before requesting a configuration-specific quotation.
Buyer questions
Do more gear ratios guarantee better coverage?
No. Review the actual input range, required output points and load limits in each gear.
Does a multi-speed gearbox imply under-load shifting?
No. Obtain the supported engagement and transition conditions for the offered mechanism.
Background and supplier contact
Power transmission standards and technical publications offers related background, not certification of the equipment in a quotation. Applicability must be checked for the project and destination.
Explore the oilfield transmission box, browse all technical resources, or visit Vance Petroleum for company information. Request a gearbox proposal with the load schedule, interface drawings and required shaft speeds.