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2. The second piston that is available is a PTFE Encapsulated one. The piston is a magnet that has PTFE moulded around it and
then machined to the appropriate conguraon. These pistons are primarily used in PTFE ow switches and also in other ow
switch bodies ( typically 316SS and Acrylic bodies ) where customer prefer a piston that does not have epoxy in the uid path;
as well as a piston that is impervious to aggressive uids and gases. This piston is highly recommended for medical applicaons.
Hysteresis on these pistons does tend to be slightly higher (10 to 15% ) than metal piston due to friconal eects, weight,
and surface adhesion consideraons. Prior to selecng this piston, uid temperatures, and uid compability with PTFE must
be taken into account because certain aggressive chemicals at specic temperatures tend to swell PTFE causing the piston to
change shape resulng in failure of the product. Stainless or PTFE retaining rings can be used with this piston.
3. The third piston that is available is a Special All-Metal piston with no epoxy ( only available in 316SS ). This piston is fabricated
in a proprietary process with only one weld seam ( leak tested ) which presents an all 316SS surface to the uid path.
This piston is recommended for those applicaons where the piston could experience a lot of cycling wear. This piston has
been tested to 250,000 cycles at 125 psi. Stainless Steel retaining rings are recommended for this piston type for low pressure
applicaons and an orice disc ( See Universal Mounng Diagram ) is recommended for high pressure ( 125 psi ) applicaons.
SPST vs SPDT
The standard unit is provided with a SPST N.O. (N.O = Normally open at rest) dry reed switch. Increasing ow past point will close
(acvate) the switch. Decrease ow will open (de-acvate) the switch).
SPST NC. (N.C = Normally close at rest) models are closed at rest. Increasing ow pass set point opens the switch and decreasing
ow to set point will close the switch( Typically used to detect loss of ow condion in overall systems)
SPDT (Single Pole Double Throw) switches have both N.O. & N.C. conguraons by using a common pole along with two addi-
onal poles to achieve this dual capability.
Conversion from N.O. (Normally Open) to N.C. (Normally closed)
1. Loosen allen set screws (4 - 40) on face of body. These are the set screws holding the reed switch in place.
2. Move the reed switch downwards unl it shows a closed contact on the mul-meter.
3. Tighten (4 - 40) allen set screws on face of the body.
4. Cycle unl on and o by turning upside down to simulate ow. This may necessitate some renement of the exact locaon
of the reed switch as determined in step 2.
Precauons during installaon
1. Avoid any foreign parcles during installaon.
2. Large metallic and/or magnec elds may aect the principle of operaon of these units. if disturbance is detected,
magnec shielding may be necessary to ensure correct operaon of the ow switch.
3. During installaon of explosion proof versions carefully screw in the conduit connector for the electrical leads piping so
as to avoid damaging the reed switch leads or reed switch capsule which may lead to shorng the switch installaon. 6 (Six
threads) have been provided for installaon.
4. Electrical rangs etc. have been discussed later in this bullen. it is advisable to keep within those rangs as excessive
power will FRY the switch.
Electrical Protecon/Rangs
The electrical Reed Switch is rated for several million cycles and should rarely require replacement. Most switch failures are
the result of overloading. DO NOT EXCEED RATED CAPACITY, as this will cook the REED SWITCH, Catalogue rangs are based
upon D.C. resisve loads, however A.C. loads are also commonly switched.
Inducve load switching- Unless appropriate contact protecon is provided with either a diode or R.C. network, inducve load
switching will cause the contacts to sck.
Capacive load switching - The stac capacitance in cables may cause permanent or intermier contact scking. Contacts may
be protected by a series surge protector of 0.5 to 5 mAH, depending on the load. in some instances, a 10-500 ohm resistor can
replace the surge suppressor.
Cleaning
Cleaning the ow switch is easily accomplished without removing from the line. By unscrewing the clean out plug, the mag-
nec piston may be removed and the ow passage ushed or cleaned. Care should be taken to thoroughly clean the piston
before replacing ( replace the piston as shown in see page 3 gure 2. if the piston is replaced incorrectly, incorrect operaon
will result).
1. A magnet may be used to remove the magnec piston.
2. PTFE end plugs (on PTFE models) should not be over ghtened.
