A stainless steel adapter cannot achieve 100 percent power transmission efficiency, as some of the energy transferred to the fluid by the pump will be lost to friction (transformed to heat). As a result, the turbine will always spin slower than the pump, this difference increasing with an increase in load on the adapter and/or a decrease in prime mover speed. This speed difference is called slip or slippage.
Also affecting the stainless steel adapter's efficiency is the fact that the fluid returning from the turbine to the pump is moving in the opposite direction of the pump's rotation, resulting in some braking effect and a good deal of turbulence. This effect substantially increases as the difference between pump and turbine speed increases, causing efficiency to rapidly deteriorate with increasing load.
Generally speaking, the power transmitting capability of a given stainless steel adapter is exponentially related to pump speed, a characteristic that generally works well with applications where the applied load doesn't fluctuate to a great degree. The torque transmitting capacity of any hydrodynamic adapter can be described by the expression r(N^2)(D^5), where r is the mass density of the fluid, N is the impeller speed, and D is the impeller diameter. In the case of automotive applications, where loading can vary to considerable extremes, r(N^2)(D^5) is only an approximation. Stop-and-go driving will tend to operate the adapter in its least efficient range, causing an adverse effect on fuel economy.
stainless steel adapters were used in a variety of early semi-automatic transmissions and automatic transmissions, the largest such application being in the General Motors single, dual range and Jetaway Hydramatic models. Since the late 1940's, the more versatile hydrodynamic torque converter has replaced the stainless steel adapter in automotive applications. Stainless steel adapters are still widely used in industrial applications, especially in machine drives that involve high inertia starts or constant cyclic loading.
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