The pump uses a mechanical type shaft seal with a Nitrile rubber element. It is suitable for water, oils, and some mild solvents and it is limited to 212o F. Fluoroelastomer (S10) seals or Polytetrafluoroethylene (PTFE) (S11) seals are available for severe solvents, difficult chemicals, and elevated temperatures. The flow of a centrifugal pump can be conveniently controlled by a throttling valve in the discharge line without the need for a relief valve. In centrifugal pumps, the horsepower demand will decrease as the pressure increases. Maximum horsepower occurs with a wide open discharge.