McDonnell & Miller Frequently Asked Questions
Q.	What water feeder should I use with your Series PS-801 or 67 Low Water Cut-off?
A.	Select a water feeder that is 1-1/2 to 2 times the steaming rate of the boiler. The Series PS-801 and 67 Low Water Cut-off will operate Series 101-A or Uni-Match Series WF2 Water Feeders.
Q.	How do I determine where to mount a pump controller in relation to the normal water line?
A.	"Pump off" should be positioned at the normal water line.
Q.	What causes the float to collapse in Series 150, 157, 193 and 194 boiler controls?
A.	Floats collapse for two reasons: 1) over pressure and 2) water hammer. Water hammer generally occurs during blow down. It sounds like snapping and crackling in the pipe.
Q.	How do I select the proper flow switch for my application?
A.	Four things should be considered: 1) flow rate, 2) pipe size, 3) pressure, and 4) the type of enclosure (NEMA Rating). Refer to the "How to Select Liquid Flow Switches" section on pages 97 - 104 or the "How to Select Air Flow Switches" section on pages 124 - 127, of the McDonnell & Miller General Catalog MM-825.
Q.	How can I prevent paddles from breaking on Series FS4-3 and FS8-W Liquid Flow Switches?
A.	First, do not use liquid flow switches on systems with flow greater than 10 feet (3m) per second. Second, the flow switch should be located five pipe diameters from any fittings or valves. And last, but not least, always use the shortest paddle that will do the job. We also offer a Stainless Steel paddle kit with reinforced paddles. It contains 1" (25mm) and 6" (152mm) paddles that are 0.025" (.64mm) thick.
Q.	What are K factors for flow switches and how do I use them?
A.	K Factors are used in adjusting paddle lengths. If the flow rate in the pipe exceeds the maximum adjustment on the flow switch, a change can be made in the paddle length. Modifying the paddle length is a simple procedure that will adapt the flow switch to a broader range of applications. Refer to page 104 of McDonnell & Miller General Catalog MM-825 for examples and details.
Hoffman Specialty Frequently Asked Questions
Q.	What is causing my "end of main" steam vents to spit condensate?
A.	Spitting usually occurs because the vent hasn't been installed at the proper location in the system. "End of main" steam vents should be installed on a dry return at least 15 inches (380 mm) ahead of any elbows, and on a pipe nipple 6 - 10" (150 to 250 mm) above the main. This problem often arises after a boiler conversion. Typically,the new, smaller boiler doesn't have sufficient storage capacity for the system, resulting in condensate backing up into the return piping. It may be necessary to install a boiler feed unit to store the condensate.
Q.	What is the best type of steam trap to use on a shell and tube heat exchanger?
A.	For most heat exchanger applications, a Float & Thermostatic (F & T) Steam Trap works best. Because our F & T Trap has a separate thermostatic element, it is able to quickly vent air from the shell of the heat exchanger. The float element modulates to drain condensate at a rate equal to the condensing in the heat exchanger.
Q.	How much lift will a steam trap provide?
A.	None. A trap does not provide lift. Lift is provided by the trap inlet pressure. Normally a 1 foot (305 mm) lift is practical for every 1 pound (.45 kg) of differential pressure. When there is a modulating regulator in the steam supply the trap discharge must drain by gravity or condensate will back up into the steam space, which may cause water hammer. When the trap discharge has a lift, a check valve must be installed to prevent backflow of condensate. Condensate lifts should be avoided if possible, since they can cause poor air venting and water hammer.
Q.	When selecting a steam trap, what differential pressure should I use?
A.	The differential pressure is the difference between the trap inlet pressure and the back pressure in the return line. The maximum differential pressure is the steam supply pressure. The trap must be selected with a seat rating that can open against the steam supply pressure. There is a maximum and minimum differential pressure that may occur. The minimum differential occurs during start up, or during operation when a modulating steam control valve is installed in the steam supply. The trap must be capable of draining the maximum condensing load that may occur at the minimum operating pressure.
Q.	When should I use a drip trap and how do I size it?
A.	A drip trap is used to drain condensation that occurs from heat loss in the steam line. For sizing information, refer to the Hoffman Specialty Steam Trap Engineering Data Manual HS-203.
Q.	What happens if my steam pressure exceeds the steam trap's rated pressure?
A.	The trap can fail shut because the rated pressure is the ability of the float or bucket to pull the pin away from the seat. For example, if the trap's rated seat pressure is 15 psig (1 bar) and the system is operating at 75 psi (5.2 bar), the trap will close and remain closed until the pressure drops to near 15 psi (1 bar). Using a higher rated trap will eliminate this problem since they have smaller diameter seat openings than low pressure seats. As long as the high pressure trap's rated capacity is sufficient for the system load, it will work fine.
Q.	What is the best way to test a steam trap?
A.	There are several methods that can be used depending on the type of trap you have: 1) the most accurate test for all types is visual inspection of what is coming through the trap, 2) use a test valve in the trap outlet tapping, 3) listen to sounds in the trap while using an automotive type stethoscope or an ultrasound device (traps that are blowing steam will have a hissing sound and traps that are passing condensate will have a gurgling sound), 4) instantaneous thermometers work well on thermostatic traps, 5) use a stethoscope to listen to bucket traps and thermodisc traps cycle open and shut.