738385-4 — Bypass Valve Repair & Overhaul

Component Overview

A bypass valve diverts air or fluid around a heat exchanger, filter, or other system element to regulate temperature, manage flow, or protect downstream components when the primary path is restricted. In pneumatic and air-management service it commonly modulates flow around a cooler or core, allowing controlled blending of cooled and uncooled streams or relief of excess pressure. Depending on design it is actuated thermostatically, pneumatically, or by a spring-loaded differential element. Principal wear and failure modes are seat and poppet wear that produces leakage, spring relaxation or fatigue that shifts cracking pressure, sticking from contamination or thermal cycling, actuator or sensing-element degradation, and corrosion of internal surfaces. These cause improper bypass timing, temperature or pressure excursions, and chatter, driving seat refurbishment, spring and seal replacement, and flow and crack-pressure testing.

Aircraft Application

738385-4 is used across multiple aircraft platforms. Contact QTC with your aircraft type and we'll confirm applicability and repair scope.

Our Repair Capability

QTC repairs and overhauls 738385-4 to the original manufacturer's specifications under our FAA and EASA Part 145 approvals. Our team — including former OEM pneumatic & air management engineers — performs teardown, inspection, cleaning, component replacement, functional testing, and certification, returning a serviceable unit with the appropriate airworthiness release. We also develop repairs for rejected and beyond-economic-repair (BER) hardware.

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Related Parts

Other bypass valve part numbers we repair — view all Bypass Valve parts →

Frequently Asked Questions