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Hot-tank radar pressure requirements can be misread when a process sheet uses absolute pressure but a quotation uses gauge pressure. A value such as 0.1 MPa is incomplete without its reference. Resolve that ambiguity before comparing the requirement with an instrument rating.
Write Hot-Tank Radar Pressure With Its Reference
Gauge pressure is measured relative to the local atmospheric pressure. Absolute pressure is measured relative to a vacuum reference. In a common set of units, absolute pressure equals gauge pressure plus atmospheric pressure. A negative gauge value can therefore describe a positive absolute pressure.
| Entry | What it means | What to clarify |
|---|---|---|
| Gauge | Pressure relative to the stated local atmosphere. | Use an explicit gauge label and identify the relevant operating condition. |
| Absolute | Pressure relative to the absolute zero reference. | Do not compare its number directly with an unlabelled gauge rating. |
| Vacuum | May describe a negative gauge value or another convention. | Request a numerical absolute or gauge value with units. |
| Range | Minimum and maximum during the process cycle. | Record the concurrent temperatures, not only two pressure endpoints. |
A Conversion Example, Not an Instrument Rating
Assume atmospheric pressure is 100 kPa for this example. A process pressure of 90 kPa absolute is then -10 kPa gauge. A requirement of 90 kPa gauge instead corresponds to 190 kPa absolute under the same assumption. Both entries contain the number 90, but they describe very different conditions.
The assumed 100 kPa atmosphere is for arithmetic only. Use the applicable site basis when converting actual requirements. Also normalise units: 1 MPa equals 1,000 kPa. Keep the original stated requirement alongside the conversion so transcription errors can be traced.
MV-RD12G has a listed pressure interval of -0.1 to 2.5 MPa. Do not infer a fully approved service envelope from those endpoints. Ask the supplier to identify the pressure reference and permissible pressure-temperature combinations for the actual connection and seal being offered.
Reconcile the Documents Before Ordering
Put process pressure, design requirement and instrument allowance in separate fields with consistent units and references. Have the responsible process and mechanical personnel resolve any disagreement. A level instrument cannot correct an undefined vessel-pressure requirement.
For cleaning and cooldown, add the relevant minimum pressure as well as the hot operating condition. Do not convert the word vacuum into a guessed value. If the plant has not established the credible minimum, leave the pressure review open rather than approving the assembly against an assumed number.
Pressure-Reference Questions
Q1. Does the -0.1 MPa endpoint confirm suitability for full vacuum?
Not by itself. Confirm the pressure reference, the minimum absolute pressure during cooldown or cleaning, and the allowable condition for the offered connection and seal at the corresponding temperature. A numerical endpoint alone does not establish suitability for every vacuum duty.
Q2. Can the quotation simply repeat the process sheet?
It should explicitly confirm or qualify the requirement against the offered assembly. Repeating an ambiguous value does not resolve the ambiguity. Require the same pressure reference in the final technical agreement.
Summary
State units, reference and concurrent temperature together. Submit the original process entries and reconciled conversions with an MV-RD12G pressure-duty enquiry so the quotation addresses a defined requirement.
