Five quotes, one enquiry, nothing to compare
A three line enquiry asks for a size, a pressure and a material. Five suppliers answer. The prices do not line up, and neither do the documents: one offered a reduced bore because the enquiry did not say full, one offered a PTFE seat because no temperature was written, one priced a shell test only because the word used was tested, and one will not bolt to the flange that is already welded into the line because the pressure was read in the other designation system. None of the five did anything wrong. The datasheet is the only part of the transaction that fixes what is being priced, and every field left out of it is a decision handed to whoever answers first.
Block one: the pressure basis, where Class 150 is not PN 16
Class and PN are two independent designation systems, and they do not convert by rounding. API 6D lists the two families side by side, and the pairs it gives are not the ones buyers assume: Class 150 corresponds to PN 20, Class 300 to PN 50, Class 600 to PN 100, Class 900 to PN 150, Class 1500 to PN 250 and Class 2500 to PN 420. A valve ordered as Class 150 and drilled to PN 16 has a different bolt circle, a different bolt count and a different facing height, so it will not mate with the flange on site. The two systems also rate from different reference temperatures, ASME B16.34 from 38 °C and EN 1092-1 from 20 °C, so the numbers printed in two catalogues are not comparable before a single degree of service temperature is added.
A specification fixes one system and one flange standard, and states the facing as well: raised face, flat face or ring joint. A project that works in PN can still be supplied with a valve designed to the ASME class and drilled to the EN pattern, but that is a decision to write down, not a detail to leave to the shop. The same sentence has to settle what the pressure number is a rating at, because a class alone is a rating at a reference temperature and nothing else, which is what the pressure class rating read from B16.34 separates before any catalogue number is used.
Block two: the bore, which is a different product
ISO 17292 covers both port designs in one document, which is exactly why an enquiry that says only DN50 does not define a product. A full port valve has a bore close to the pipe internal diameter and passes a cleaning pig; a reduced bore valve has a smaller bore, usually a shorter face to face dimension in the same size and class, and a lower price. The two are not interchangeable in a pigged line, in a line where the pressure drop has been calculated against the bore, or in a line where a pig has to pass a valve at all.
The datasheet should state full or reduced, and where the answer matters it should state the bore dimension rather than the nominal size. Reduced bore is a family of designs and not a fixed ratio, so two suppliers can both answer reduced bore and ship two different flow areas. A nominal size defines the connection; it does not define the passage.
Block three: the temperature that sets the real ceiling
The class on the flange is a rating at a reference temperature. The rating in service comes from the pressure temperature table of the body material, and the ceiling of the whole valve usually comes from the soft parts, which sit lower than the body. A PTFE seat is rated to 180 °C, PPL to 280 °C and PEEK to 260 °C, so a Class 300 valve with a PTFE seat is not a Class 300 valve at 250 °C, whatever the body is made of. The valve may also be derated at the top of its range by the body material rather than by the seat, and the lower of the two governs.
Two suppliers reading the same enquiry will quote two different seat materials unless the operating temperature and the design temperature are both written. The design temperature is the one that counts during procurement, because it covers the excursion the line will see once, and an excursion is what destroys a seat that was chosen on the normal operating figure. State whether the number is the medium temperature or the ambient temperature, and state it as a maximum rather than a typical. The seat material comparison is the field that most often explains a price difference between two otherwise identical offers.
Block four: the test, written as standard, medium and rate
Tested is not a requirement. A ball valve is normally given a shell test at 1.5 times the rated pressure and a seat test at 1.1 times, both to API 598, and the acceptance is a leakage rate in ISO 5208 rather than a word. Rate A is no visible leakage; the lower rates allow a measured quantity that depends on the size and the standard. An enquiry that does not name the rate gets whatever the supplier uses as a house standard, and two valves that both passed can sit a whole rate apart.
The medium matters as well, because water and gas do not prove the same thing about a seat, and the duration matters because a weep along a scratch shows in a long test and disappears in a short one. Write the standard, the medium, the multiplier and the acceptance rate in the same block, and state whether the test report travels with the valve. A buyer who writes only the pressure has bought a proof of strength, not a proof of tightness, and the two are tested separately for that reason. The ISO 5208 leakage classes are the vocabulary this block needs.
Block five: the end connection and the facing
Flanged, butt welded, socket welded and threaded are four products with four price levels and four installation procedures. Flanged is not complete without the facing and the drilling standard, because a ring joint facing takes a different gasket, needs a different groove finish and cannot be substituted with a raised face at site. A butt welded end is not complete without the pipe schedule, because the wall thickness at the weld preparation has to match the pipe, and a valve built for one schedule will not weld to a heavier pipe without a transition piece.
On a buried or fully welded line the end connection also decides whether the body has a joint that can be opened at all, which is the difference between a repair and a cut out. That is a maintenance decision disguised as a piping decision, and it belongs on the datasheet rather than in a later conversation.
Block six: the operator interface and the document package
The operator is a separate specification from the valve, and a large share of the disputes at delivery are about it. A valve with a lever, a valve with a gearbox, a valve with an ISO 5211 mounting pad and no operator, and a valve with an actuator fitted and tested are four different line items. The pad size has to be written even when the actuator comes from a third party, because the pad is machined at the factory and cannot be added convincingly later.
The document package behaves the same way. A material certificate to EN 10204 3.1 for the pressure containing parts, a fire test certificate to API 607 where the service asks for one, a NACE MR0175 statement where the service is sour, and an approval drawing before manufacture are four separate requests, and none of them is implied by the word certificate. A purchase order that asks for documentation without naming the document type usually receives a certificate of conformity, which certifies that the valve conforms to itself.
The words that do not mean the same thing twice
Most of the mismatch between two quotes sits in a small set of words that both sides believe they understand. The table is the practical version: the entry as buyers usually write it, the readings it allows, and the entry that closes the reading.
The medium is a specification field, not a context
Wet gas, sour gas, chlorine, oxygen, seawater and glycol are six media that change the material list, and none of them is implied by the words carbon steel or stainless steel. A line that carries wet hydrogen sulphide brings NACE MR0175 into the valve, and that is not a material grade but a set of rules about hardness, heat treatment and verification, which reaches the ball, the stem and the bolting as well as the body. Dry chlorine and wet chlorine point at different materials for the same valve, because the dry gas is handled by carbon steel and the wet one is not. Oxygen adds a cleanliness level and a prohibition on certain lubricants that no general purpose datasheet asks about.
The consequence for the document is that the medium line is not a description, it is a switch. Write the composition or the service name and the other five blocks adjust to it; write a generic word and every supplier makes the adjustment differently. A buyer who writes natural gas for a stream that contains carbon dioxide and water has written a different product from the one the line needs, and the datasheet is where that difference is still cheap to correct.
What to attach instead of writing more text
Three attachments do more than a page of prose. The first is the datasheet with the six blocks filled in, even where an answer is a range, because a range is a requirement and a blank is an invitation. The second is a marked up view of the mating flange or the pipe, which settles drilling, facing and weld preparation in one drawing. The third is the service described in the language of the medium: what flows, at what temperature, at what pressure, dry or wet, clean or abrasive, and whether the line is pigged.
A supplier who receives those three can quote a valve that fits. A supplier who receives a size and a class can only quote a valve that exists, and the difference between those two outcomes appears four months later on site. The API 6D and ASME B16.34 summary is the reference most of these entries are traced back to, and where a project mixes standards, the datasheet is the only place the mixture is recorded.
Where the datasheet ends and the drawing begins
Some fields cannot be written as text and should not be forced into one. Face to face dimensions, the exact bore, the seat pocket geometry and the mounting pad position belong on a drawing, and the datasheet should point at the drawing rather than paraphrase it. A datasheet that carries a dimension transcribed by hand is a datasheet that can disagree with the approval drawing, and at that point there are two specifications and no way to decide which one was bought. Where the size and class come from a standard table, name the standard and the table; where they come from the project, attach the drawing. A datasheet is a set of pointers to decisions, not a container for every number.
Checking the quotes against the document, not against each other
When the answers come back, the comparison is not the total. Read each quote against the datasheet block by block: pressure basis and flange drilling, port, seat material against the stated design temperature, test standard and acceptance rate, facing, operator and documents. Any block answered differently from the enquiry is either a clarification to be resolved or a scope difference that explains the price.
Sorting five quotes this way usually removes most of the spread and leaves one or two genuine commercial decisions. It also produces a record of what was bought, which is the document that gets read when a valve leaks four years later and nobody remembers what was ordered. The drivers of ball valve lead time follow the same pattern: the fields that decide the schedule are the ones fixed early and rarely written down.
Frequently Asked Questions
Is ASME Class 150 the same as PN 16? No. API 6D pairs Class 150 with PN 20 and Class 300 with PN 50, not with PN 16 and PN 40. The two systems use different reference temperatures and different flange drilling, so a Class 150 valve and a PN 16 flange will not necessarily bolt together. A datasheet has to name one system, one flange standard and one facing.
Does a ball valve datasheet have to state the bore? Yes, as full port or reduced port at minimum, and as a dimension where the flow area matters. ISO 17292 covers both designs, so a nominal size alone defines the connection and leaves the passage open. Reduced bore is a family of designs rather than a fixed ratio, which is why two suppliers can both answer reduced bore and ship different flow areas.
Which temperature belongs on the datasheet? Both the operating temperature and the design temperature, and it has to be clear which is which. The design temperature covers the excursion the line will see once, and it is the figure that decides the seat material, because a PTFE seat rated to 180 °C, PPL to 280 °C and PEEK to 260 °C sets the ceiling of the valve before the body material does.
Is it enough to ask for a tested valve? No. Name the standard, the medium, the multipliers and the acceptance rate: a shell test at 1.5 times and a seat test at 1.1 times to API 598, accepted at a stated ISO 5208 rate. Two valves that both passed a test described only as tested can be several leakage rates apart, and only one of them will hold in the service the line was designed for.
