Sonic conductance C on a pneumatic valve quotation needs context. Keep the coefficient, its unit, the accompanying pressure-ratio data and the exact component reference together. A single number copied into an equipment comparison leaves too many questions unanswered.
For an aluminum cutting project, use this guide when a supplier sends a valve data sheet with a machine proposal. The aim is to produce a clear document review that an engineer can complete, rather than ask a buyer to approve a component from one catalog value.
Start with these three checks
- Keep C and its unit together with the stated definition of b.
- Record the pressure basis and the conditions behind the comparison.
- Match the data to the complete component and the proposed application.
1. Read sonic conductance C alongside b
SMC’s technical guide defines C from choked mass flow divided by upstream absolute pressure and reference density. Its displayed unit is dm³/(s·bar). The guide defines b as the critical downstream-to-upstream absolute pressure ratio. In the illustrated model, a ratio at or below b belongs to the choked branch; above b, it belongs to the subsonic branch.
The guide is historical and cites ISO 6358:1989. Use the definitions to understand the document, then request the applicable method and edition for the offered component. This article does not establish compliance with a current standard.
Source: SMC technical data, Solenoid Valve Flow Rate Characteristics.
Keep a small evidence folder for each offer. It can contain the original data sheet, the quotation reference and the supplier’s written clarification. Name each file so someone reviewing the purchase next month can find the same evidence without searching an email chain.
If a quote says only “C = 1.2,” send a focused question: “Please provide the unit, associated b value and the original data sheet for this exact offered component.” Leave the comparison cell pending until the reply identifies those items.
2. Preserve the pressure basis in the comparison
Before calculating anything, put the pressure labels on the worksheet. Preserve the supplier’s notation. If a pressure basis is omitted, request clarification rather than silently interpret the number.
The following example uses invented values. It is a reading exercise with both pressures explicitly absolute, not a proposed machine setting or a measured result.
| Fictional record | Value for this exercise |
|---|---|
| C for both candidates | 1.2 dm³/(s·bar) |
| Upstream absolute pressure | 0.60 MPa |
| Downstream absolute pressure | 0.24 MPa |
| Candidate A: b | 0.30 |
| Candidate B: b | 0.50 |
The exercise gives a pressure ratio of 0.24 ÷ 0.60 = 0.40. In the cited model, A is on the subsonic branch because 0.40 exceeds 0.30. B is on the choked branch because 0.40 is below 0.50. Equal C values have not made these two records identical.
This exercise does not calculate delivered flow, choose a winner or predict cylinder motion. Put those questions into the engineering review of the actual proposal. Do not carry either fictional candidate into the approved bill of materials.
Use separate columns for supplied facts and your calculations. A reviewer should immediately see which figures came from a vendor and which were created by the purchasing team. Mark unresolved inputs visibly, rather than making a completed-looking table with assumptions hidden in footnotes.
3. Tie the coefficients to the complete offered component
Copy the full component designation from the quotation. Ask the supplier to identify the corresponding line in the data sheet. A cropped screenshot is difficult to review when the row heading, document revision or option code is missing.
For an equipment purchase, add a document index to the technical discussion. Identify the quotation revision, component reference, supplier evidence and the person assigned to answer each open question. This makes the decision traceable without turning the purchase sheet into a substitute engineering specification.
Keep the review scoped to the actual equipment arrangement. Ask the machine supplier to explain how the offered component fits the proposal and what application information is still required. A general catalog page is useful background; the written response must identify the offered configuration.
If two suppliers submit different formats, retain both originals. Build a shared comparison sheet around agreed fields, then invite each supplier to correct its own entry. Do not delete qualifications to make the rows look symmetrical.
A concise clarification request
You can adapt this message to an actual quotation:
Please identify the exact valve reference in offer [revision]. Provide the original data sheet and the C unit, associated b definition, pressure basis and applicable conditions. Please also identify the responsible engineering contact for confirming the component’s suitability in the proposed machine arrangement.
Attach the marked quotation page. Keep one question number for this issue so the reply can be linked to the original request. If a revised component is proposed, ask for a revised offer instead of treating an informal email as the final purchase record.
The wider site utility review is covered in compressed air for aluminum saws. For a different document question about actuator calculations, see pneumatic cylinder force. Keep those workstreams identifiable in the equipment review.
Common purchasing questions
Can I approve a quoted valve from C alone?
Keep the approval pending until the offer includes the complete component reference and supporting documentation. Ask the responsible engineer to review the application. This guide provides a way to organize that discussion.
What if the supplier sends a different document after clarification?
Record the new revision, retain the earlier copy and identify what changed. Ask whether the updated evidence changes the offered component or simply completes missing information.
Should the fictional pressure example go into my RFQ?
No. Use your actual project information and have its basis checked. The example exists only to show why an apparently complete comparison still needs careful reading.
Prepare a useful machine inquiry
Send JiurunCut your profile drawing, material description, desired finished parts and the equipment questions you want reviewed. If valve documentation is part of the discussion, attach the complete supplier file and mark the unresolved field.
Contact JiurunCut with your drawing and project requirements. A clear inquiry allows the proposed machine and its supporting documents to be discussed together.