These ball valves were cut away to show how such valves are designed and constructed. Like stopcocks, ball valves are designed with a drilled plug that rotates between two in-line ports in the valve body. The major difference between a stopcock and a ball valve is that when the ball valve is in the closed position, the pressure of water behind the ball presses the ball into a round seat. This design makes it possible for ball valves to compensate for wear and expansion in most applications. However, when ball valves are used in very low pressure applications, such as water containers, this feature is of little consequence, and the valves must depend on the ball being squeezed between two seals in order to affect a seal.
Ball valves have all the problems of stopcocks and needle valves.
And ball valves have very large dead-spaces, which are in direct contact with the water stream as their balls rotate during opening and closing and the holes cross the seals. Testing for endotoxins is a quick, sensitive, and cost-effective way to learn a great deal about the condition and performance of laboratory water purification systems with regard to organics and microorganisms. Initial microbial growth and establishment of biofilms in purified water are attributed primarily to ubiquitous gram-negative bacteria, the source of endotoxins. Gram-negatives grow in very low concentrations of organic carbon and respond by increasing cell size and growth rate when the concentration of organic material in their environment increases. When direct TOC testing is not available on a regular basis, endotoxin testing can help to bridge the gap by providing indirect approximations of TOC levels.