You do not need a perfect inventory. You need six columns and an honest note about condition.
Start with what the stores system already has
Most plants already hold the data in an ERP or CMMS export: part number, description, quantity, location and sometimes the original purchase date. That export, filtered to valves, is the best possible starting point and takes minutes to produce.
Do not spend a week cleaning it. Send it with the obvious duplicates removed and a note about which rows are uncertain.
The six columns that matter
Size, pressure class, valve type, body material, operator type and quantity. Add condition and tag number if you have them. That is the whole specification for most standard valves.
For control valves add the actuator model and positioner model. For relief valves add set pressure and orifice. Those three additions cover most of the high-value items.
Photographs instead of a list
If there is no system data, photographs work. One wide shot per shelf or pallet, one plate shot per distinct model, and a note of how many of each. A crib of two hundred valves can be documented in half an hour this way.
Write the quantity on a piece of paper and include it in the wide shot. It saves a round of questions later.
Say what is wrong
Note the damaged items, the incomplete assemblies, the valves that have been outside for years and the ones nobody can identify. A list that flags its own problems is faster to price than one that claims uniform quality, because the second list has to be verified.
Mixed lots, partial assemblies and valves needing repair are all normal. They do not need to be removed from the list before sending it.
One list, one review
Send everything in one go, even if it comes from several buildings or several sites. A single review produces a single offer and a single collection, which is almost always better value than several small transactions.
If the material is at multiple locations, say where each part is. We can consolidate.
Questions sellers ask
What format should the list be in?
Anything readable: Excel, CSV, PDF, a photograph of a handwritten sheet, or the body of an email.
How long should the list take to prepare?
An ERP export takes minutes. A photographed crib takes about half an hour. It should not take a day.
Do you need weights and dimensions?
Only for very large valves, where transport planning matters. We can establish those ourselves.