When we are designing the mechanical seal with sleeve on a shaft or making a stepped shaft, we balance the forces which are acting on the sliding surfaces. By that we could arrange higher P-v values. We call this the "balanced mechanical seal" BT-1 type is mostly used in water pumps and central heating pumps and it’s very rugged and reliable. Combination of seal face materials is designed for working condition and pumping media. Secondary sealing by O-ring. Other construction parts are made of stainless steel.