The Mixer RFQ Checklist: 10 Details Engineers Need for a Useful Quote

Picture this: you sent a mixer quote request to three vendors. Two came back within a week. The third came back three weeks later, along with a list of follow-up questions you could have answered on day one. Often, the difference is the information included in the original RFQ.

Many avoidable quote delays begin with missing application inputs. Viscosity, specific gravity, tank geometry, batch size. Without those inputs, an applications engineer can't size a motor, select an impeller, or specify a seal with any confidence. They have to make assumptions or request more information, and either one can delay the quote.

What Goes on a Complete Mixer RFQ

To give the applications engineer a stronger basis for the quote, provide these 10 inputs. They fall into five groups:

• Product behavior: viscosity range from start to finish, specific gravity, solids content, and shear sensitivity
• Batch and vessel: normal and maximum working volume, total tank volume, and tank dimensions
• Operating conditions: the full temperature range the product sees during mixing
• Build requirements: sanitary construction and surface finish
• Site conditions: power supply (voltage, phase, frequency) and hazardous area classification

Complete information doesn't guarantee a quote by Friday. What it does is reduce the assumptions the engineer has to make and the follow-up questions you have to answer.

Why an Incomplete RFQ Can Cost More Than Time

An incomplete RFQ doesn't just slow things down. It can also push the design in a direction you didn't intend. When viscosity is missing, for example, the engineer has to assume a value, and most will assume conservatively to protect the equipment. Depending on the application, that can mean a larger motor, a heavier shaft, a longer lead time, or a higher price than your process actually requires. The cost of a missing spec isn't only the wait. It can be money committed to equipment sized for conditions you don't have.

Four Inputs That Commonly Lead to Follow-Up Questions

When an RFQ comes back with questions instead of a quote, it's often because one of these four inputs was missing.

Viscosity. Viscosity is an important input for motor sizing, impeller selection, and shaft design. Without a number, or at least a range, the engineer has to assume one, and a conservative assumption may increase equipment size or cost while leaving the proposal dependent on conditions that haven't been confirmed.

Specific gravity. Specific gravity (SG) feeds directly into torque and power calculations. A product that pours like water but has an SG of 1.3 carries more mass through every impeller rotation. A higher specific gravity can affect the required motor power and should be part of the design basis.

Tank geometry. Impeller diameter and shaft length are determined relative to tank diameter and liquid depth. Without dimensions, impeller selection is a guess. A mixer sized for a 48-inch diameter tank won't necessarily perform the same way in a 36-inch tank.

Batch size. Working volume and tank capacity aren't the same thing. A 500-gallon tank running at 60 percent fill has a different mixing requirement than one running full, and the liquid level affects shaft length and impeller placement too.

The 10 Inputs Every Mixer RFQ Needs

1. Product and viscosity range (start to finish). Give the viscosity at the beginning and end of the process, not just at ambient temperature or at the target. A dissolution, a polymerization, or an emulsion that builds body as it forms can start thin and finish thick. Describe that behavior along with the full range, and the engineer can design for the whole batch instead of one snapshot of it.

2. Specific gravity. State the SG of the product at operating conditions. If you don't have a measured value, say so rather than leaving the field blank, and note any provisional assumption you'd like the engineer to review. An incorrect SG can lead to a motor that is undersized for the actual load.

3. Batch volume. Provide the normal working volume and the maximum working volume, along with the total tank volume, so the vendor can size the mixer to the intended operating range. If your working volume varies from batch to batch, give the range.

4. Tank dimensions. Diameter and straight-side height at a minimum. Tank geometry informs impeller diameter, shaft length, and where the impeller sits in the liquid. The right proportions vary widely by impeller type and mixing objective, so a hydrofoil and an anchor are sized very differently for the same vessel. If you have a drawing or a spec sheet for the tank, include it, since bottom shape, nozzle locations, and existing mounting flanges all matter.

5. Operating temperature. Give the full temperature range the product sees during mixing, not just ambient. Temperature can affect viscosity, seal material compatibility, gearbox lubrication, and materials of construction. If the product is heated or cooled in the vessel, or generates heat as it reacts, say so.

6. Solids content. Percentage by weight or by volume, plus particle size and density if you have them. Suspending or dissolving solids is a different mixing objective than blending two liquids, and it changes how the impeller and drive are selected. Abrasive solids also affect shaft and seal selection and can shorten component life if they aren't accounted for in the design.

7. Shear sensitivity. Is the product shear-sensitive? This matters because the wrong mixing conditions can damage some products, such as a delicate emulsion, a live culture, or a structured gel. If you aren't sure, describe what the finished product should look like and how it behaves today, and let the applications engineer ask the follow-up questions.

8. Sanitary and finish requirements. Do you need CIP compatibility? An electropolished interior? Equipment built to 3-A Sanitary Standards, or materials of construction that meet FDA food-contact requirements? Each of these affects cost and lead time, so be specific about which ones apply. A food-grade application with a Ra 32 microinch interior finish and CIP spray coverage is a different build than standard industrial stainless, and the quote should reflect that difference.

9. Power and voltage. Give the site voltage, phase, and frequency at the panel that will feed the mixer, for example 460V, 3-phase, 60 Hz. Don't assume the vendor will guess correctly, especially for export projects or older facilities. Getting this wrong can mean a motor that can't be wired without a transformer or a drive that needs modification. Confirm at the panel before submitting the RFQ.

10. Hazardous area classification. If the application involves flammable solvents, vapors, or combustible dusts, provide the hazardous location classification for the area where the mixer will be installed: the Class, Division, and Group under the National Electrical Code (NEC), or the Zone designation if your facility uses the zone system. This is not the same as a NEMA enclosure rating, which describes the enclosure itself. The classification determines whether the motor, drive, and controls need to be rated for that location. Equipment rated for a classified location is a different build from a standard TEFC motor and panel, with its own lead time and price.

If you're unsure about any of these inputs, describe what you know. Our applications engineers at MXD Process can help you work out the rest before the RFQ is submitted. Ask an engineer.

How to Estimate Viscosity If You Don't Have a Lab Number

Viscosity is sometimes left blank when a measured value isn't available. A measured value, or a product sample we can test in our lab, is always the best input. If neither is possible, a reasonable estimate is better than nothing. The reference points below are illustrative only. They're approximate, they're temperature-dependent, and they're meant to help you describe your product, not replace a measurement.

• Water: about 1 cP
• Vegetable oil: about 50 cP
• Motor oil (SAE 30): roughly 100 to 200 cP
• Honey: roughly 8,000 to 10,000 cP
• Peanut butter: roughly 150,000 to 250,000 cP

Alongside a number, describe how the product behaves. Does it pour easily at room temperature? Does it take real effort to stir? Does it hold its shape when it sits? Those descriptions give the engineer something to work from and something to confirm.

Precision matters here because the range is enormous. A mixer selected for a 10 cP product may be unsuitable at 5,000 cP, because motor load, shaft torque, and impeller requirements can change substantially across that range. The reverse is also true: a mixer built for 5,000 cP may be more machine than a 10 cP product needs.

If your product changes viscosity during mixing, which is common in emulsification, polymerization, and dissolution, give both the starting and ending viscosity and describe when the change happens. If you can't estimate a number at all, describe what the product does: "it pours like water," "it stays on the spoon," "it flows slowly when tilted." A good applications engineer can work from a description.

How to Compare Quotes Apples to Apples

If you're getting quotes from multiple vendors, confirm that you're comparing the same thing. Four elements that commonly make mixer quotes difficult to compare:

Torque basis. Two quotes for a "5 HP mixer" can deliver very different output torque at the shaft, depending on gear ratio and output speed. Ask each vendor to state motor horsepower, output speed, and rated output torque at the shaft so you can compare the drives on the same basis. We go deeper on torque versus horsepower in our post on common mixer specification mistakes.

Impeller type and diameter. A pitched-blade turbine and a high-efficiency hydrofoil are both axial flow impellers and can both be offered for the same application, but they won't necessarily perform the same way. Ask each vendor to specify impeller type, diameter, and number of blades.

Seal type. Lip seals and mechanical seals are different seal types, and a magnetic drive is a sealless alternative to both. Each has a different cost, maintenance, and containment profile. A quote that doesn't name which one is included isn't complete.

Surface finish. An electropolished, passivated 316L interior isn't the same as a mill-finish 304 interior. If the finish specification isn't stated on both quotes, the lower price may simply be the one that left it out.

If these specifications differ or are missing, the prices aren't yet directly comparable.

Common RFQ Mistakes That Slow Down the Quote Process

• Providing a single-point viscosity instead of a range. Many mixing processes change viscosity over the batch, so give both ends.
• Assuming the vendor knows your site voltage. They don't unless you tell them, so confirm at the panel.
• Leaving out hazardous area classification because the application probably doesn't need it. If there is any flammable vapor or combustible dust present, confirm the classification before it becomes a field problem after installation.
• Specifying a sanitary finish on equipment that doesn't need one. Electropolish and 3-A construction add cost and lead time, so leave them off if your process doesn't require them.
• Listing tank capacity instead of working volume. They aren't the same number, and they produce different mixer specs.
• Treating "I'm not sure" as a reason to leave a field blank. A description, a range, or a flagged assumption gives the engineer far more to work with than an empty line.

What a Complete Mixer RFQ Actually Does

A complete RFQ isn't paperwork for its own sake. Providing these 10 inputs gives the applications engineer a stronger basis for the quote and can reduce the assumptions and follow-up questions that stretch a one-week turnaround into three. It also gets you a quote for the mixer your process actually needs, not a conservative guess at it.

Submit Your Mixer RFQ to MXD Process

If you've waited weeks on a quote, or received a mixer sized for a product you don't make, the fix starts with the RFQ. Use the MXD Process Mixer Quote Form and include the 10 inputs above. If you're unsure about viscosity, solids behavior, or hazardous area classification, describe what you know. Our engineering team will ask the right questions from there, and if the application calls for it, we can test a sample in our lab before anything gets sized. For the questions to ask once the quotes come back, see our industrial mixer FAQs. Here to help, from beginning to end.