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Product Type
Accessory
Solution
Hydraulic Oil Cooling
Thermal Bypass Valve — Return-Line Oil Temperature Control for Hydraulic & Hydrostatic Circuits
The Thermal Transfer Products Thermal Bypass Valve is a return-line temperature-control valve for hydraulic and hydrostatic drive circuits that require fast warm-up, controlled fluid temperature, and low return-line back pressure. Installed in the return line of a hydraulic circuit that uses an oil cooler, it automatically modulates fluid temperature by shifting return-line flow through the cooler once the oil is warm, or bypassing it directly to the reservoir during cold start-up.
When the oil is cold (below about 110°F / 43°C), the valve directs flow around the cooler with minimum pressure loss, letting the oil reach operating temperature faster and preventing overcooling. Once the oil warms past the set point, the thermal element closes the bypass and sends full flow through the cooler. A built-in pressure relief function (set at 60 PSI) automatically relieves excess pressure to the reservoir if the cooler becomes restricted or the pressure drop climbs too high — protecting the cooler from cold-oil surges and blockage.
The valve activates at a nominal 110°F (43°C) and integrates directly with TTP’s MA, MAR, and BOLR Series hydraulic oil coolers to form a complete, temperature-controlled cooling system. By holding oil at its optimal temperature and eliminating cold-start stress, it reduces energy loss, minimizes component wear, and extends system life. TTP Application Engineering can help select the right valve for your flow rate, oil viscosity, and temperature-control needs.
Consult catalog for additional sizes and technical information.
Documents
Brochures
Thermal Bypass Assembly
Brochures
Thermal Bypass Assembly
Frequently Asked Questions
It’s a return-line valve that automatically controls hydraulic oil temperature by routing return flow either through the cooler (when the oil is warm) or straight to the reservoir (when it’s cold) — giving faster warm-up and low back pressure without any electrical controls.
Below about 110°F (43°C) the valve keeps the P-T path open, bypassing the cooler with minimal pressure loss so the oil warms quickly. Once the oil passes 110°F, the thermal wax element closes that path and directs full flow through the cooler for cooling.
It’s set at 60 PSI and automatically relieves excess pressure to the reservoir if the cooler becomes restricted or the pressure drop gets too high — protecting the cooler during cold starts and return-line flow surges.
Hydrostatic drive circuits and hydraulic systems that need fast warm-up, controlled fluid temperature, and low return-line back pressure — especially equipment exposed to cold environments or frequent start-ups.
It integrates directly with TTP’s MA, MAR, and BOLR Series hydraulic oil coolers to create a complete, temperature-controlled cooling system, and can be applied to other cooler circuits as well.
This thermal bypass valve installs in the hydraulic return line and combines temperature bypass with a 60 PSI pressure relief, tuned for low back pressure in hydrostatic circuits. The three-way thermostatic valve is a separate diverting/mixing valve (110°F or 140°F settings, ½”–2″ NPT) for broader oil or water temperature control. Choose the thermal bypass valve for return-line hydraulic warm-up and cooler protection; the three-way valve for general diverting/mixing temperature control.
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