así yo lo traduciria

Today's Technician: Automatic Transmissions and Transaxles
https://books.google.co.uk/books?isbn=1133007627
Jack Erjavec - 2010 - ‎Technology & Engineering
When a spool valve is controlled by a spring and hydraulic pressure, the tension of the spring ... A relay valve is used in many torque converter clutch circuits.
Organizational, direct support and general support ...
https://books.google.co.uk/books?id=fqYXAAAAYAAJ
1987 - ‎Loaders (Machines)
The pressure in the spring chamber and the force of the springs moves the valve to the left against the speed clutch pressure at the left end of the valve spool.

This is part of a hydraulically actuated clutch. The hydraulic system consists of a master cylinder actuated by the clutch pedal and a slave cylinder actuated by the pressure supplied by the master cylinder (bomba). The function of the spring is to return the cylinder piston to its neural position when the pressure is released (when you take your foot off of the pedal). Hydraulic brakes are similar except that there are four slave units (cylinders for drum brakes, calipers for disc),

unfortunately this link doesn't work
www.google.com/patents/US3321913Google
in a preferred use, the clutch slave cylinder is part of a hydraulic control system for a spring-loaded friction clutch. The cylinder is linked to a clutch through a ...


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Note added at 2 days4 hrs (2016-04-10 00:42:15 GMT)
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Disregard this answer. I conflated bobina with bomba.

Bobina de muelle would be coil spring. It probably refers to the coil springs in the clutch pressure plate assembly.