a) ball valves 　　　Positive Features – Recommendations 　　　1) Bubble-tight shut-off from resilient (TFE) seats 　　　2) Quick 90° open/close, not torque-dependent for seating 　　　3) Straight-through unobstructed flow, bidirectional 　　　4) Minimal pressure drop if full-port selected 　　　5) Can be throttled (Application dependent) 　　　6) Easier to automate than multi-turn valves 　　　7) More compact than multi-turn valves 　　　8) Offers high cycle life 　　　Disadvantages 　　　1) Temperature range limited by seat material 　　　Body Styles 　　　1) One-piece has no potential body leak path, but requires use of reduced port ball; thus, significant pressure drop. Not repairable. 　　　2) Two-piece end entry is most common in building services. Best price value. Available full- or standard-port balls. Not recommended to be repaired. 　　　3) Three-piece is more costly, but is easier to disassemble and offers in-line repairability. Available in full- or standard-port balls. 　　　4) Top entry is preferred in some industrial applications where access for repair is required without removing body from the line. More costly than two-piece style. 　　　Port Size 　　　1) Full-Port ball valves provide pressure drop equal to equivalent length of pipe, and even slightly better than gate valves. 　　　2) Standard (conventional) port balls are up to one pipe size smaller than nominal pipe size, but still have significantly better flow than globe valves. 　　　3) Reduced port ball valves have more than one pipe size flow restriction and are not recommended in building services piping, but rather for process piping in hazardous material transfer. b) butterfly valves – Resilient Seated Positive Features – Recommendations 1) Bubble-tight shut-off from resilient seats 2) Quick 90° open/close, easier to automate than multi-turn valves 3) Very cost-effective compared to alternate valve choices 4) Broad range of throttling capabilities 5) Nearly full flow, less pressure drop than globe valves 6) Broad selection of trim materials to match different fluid conditions 7) More compact than multi-turn valves 8) Offers high cycle life Disadvantages 1) Not for use with steam 2) Gear operators needed larger than 6” to aid in operation and protect against operating too quickly and causing destructive line shock. Body Styles 1) Wafer-style held in place between two pipe flanges. Easy to install but cannot be used as isolation valve. 2) Lug-style is a wafer body but has tapped lugs matching up to bolt circle of Class 125/150 flanges. Easily installed with cap screws from either side. Lug-style designs from some manufacturers permit dropping the pipe from one side and the valve will hold full pressure when needed. (Dead end service) 3) Grooved butterfly valves direct connect to pipe using iron pipe size couplings. Grooved valves are easiest to install. 4) Flanged butterfly valves face to face dimension conforms to ANSI Standard B16.10 and