Evaluating damper bids is difficult because the documents are usually inconsistent between suppliers. A bid that includes the right six items can be assessed in an afternoon; one that includes only a catalogue page cannot be assessed at all.
1. General arrangement drawing
Dimensional, with the flange drilling, the shaft centres, the actuator envelope including removal clearance, the weight and the lifting points. Without the removal clearance the drawing is not usable by a maintenance planner, which is the person who will actually live with the gate.
2. Duty data sheet
Design temperature, design pressure difference, medium and dust load, operations per year, and the assumed leakage figure. The leakage figure should be a number with a test condition attached, not "tight". A bid that says "zero leakage" without stating how it was measured is telling you something about the supplier.
3. Material specification
Grade for each component: frame, blade, shaft, seat, sealing strip, fasteners. Not "stainless steel". The shaft in particular should be called out separately, because it is the part that cannot be inspected without opening the duct and it is the part most often downgraded to save cost.
4. Actuator data
Type, torque or thrust, stroke time, fail position, protection class, area classification and the make and model. A named actuator can be checked; "electric actuator, quality brand" cannot.
5. Test and inspection plan
What will be tested, at what pressure, and what documents will be issued. Pressure test certificate, dimensional report, material certificates to EN 10204 3.1, and the blade travel record with the torque at the tightest point.
6. Setting and maintenance manual
Commissioning sequence, limit switch setting procedure, greasing points and intervals, spare parts list with recommended first spares. This document is written once and used for fifteen years, and its absence is the reason plants end up calling the supplier for a fifteen-year-old gate.
What to do with a bid that has all six
Compare the leakage figures at the stated condition, the actuator torque against your calculated requirement, and the shaft material. Those three comparisons will separate the bids more reliably than the price column, because the price difference is usually made up of exactly those three items.