You need a double-float Buchholz relay of type 10 (BF 80/Q) with one cable gland of M20 x 1.5 and one dummy plug. The damper should respond at a insulating liquid flow of 1.50 m/s. The upper switching system should be equipped with one switching element (magnet contact tube) and the lower with two switching elements (magnet contact tubes). The upper switching element should be designed as one normally open contact, and the lower as two normally open contacts. The device should be delivered in colour RAL 7033 and should have one oil drain plug.
Accordingly the relay ordered has the following
 

type code: 10-1.25.28.44.-0313

Explanation:
10 = Double-float Buchholz relay type 10 (BF 80/Q)
1 = M20x1.5: 1 cable gland and 1 dummy plug
25 = Lower switching system equipped with 2 magnet contact tubes
28 = With oil drain plug
44 = Casing colour RAL 7033 (cement-grey)
03 = Damper setting: 1.50 m/s ± 15 %
1 = Contact setting of upper switching system: 1 normally-open contact
3 = Contact setting of lower switching system: 2 normally-open contacts