Operating instruction for metal diaphragm type FlexOrber pulsation dampeners.
Jacketed FlexOrber Metal Diaphragm "Jkt-FLo-MD"
1. FlexOrber -MD, Design constraint; how this impacts dampner choice, installation and use.
Metal diaphragms, that are flat, may only deflect by 1 (one) degree above and below their flat, as clamped, unstressed condition. This constraint on their amount of movement causes any need for volume change deflection to result in a large diameter metal diaphragm. As the major need for volume, of any accumulator type dampner, is to house a compressible gas, usually nitrogen, in a separate chamber (1) into which the metal diaphragm does not typically deflect because it is controlled in its travel by stroke limiting plates (2).
In order to reduce the diameter of the diaphragm housing, to control cost, the diaphragm is often itself “corrugated” or “convoluted”(3). This method may comparatively increase the available deflection angle for any diameter of diaphragm without reducing its life. Because of these cost control features (1) (2) (3) above, the metal diaphragm must be caused to cycle between its stroke limiting plates without beating on them, because any impact against the stroke limiting plates will limit the life of a metal diaphragm.
2. Pre-Filling (a.k.a.”precharging”) a metal diaphragm dampner.
Pre-Filling a dampner that has a metal diaphragm is critical to ensuring that the diaphragm is not cycled against the stroke limiting plates.
A. The temperature of the pre-fill Nitrogen (O.F.N.) must be the same as the system liquid. As one major application for these PulseGuard FlexOrber metal diaphragm dampners is for systems in which the temperature is above that at which an elastomeric membrane, or PTFE plastomeric diaphragm can be used; the pre-filling process is often a multi-step procedure.
i. Pre-fill the dampner to the expected theoretical system liquid pressure.
ii. Connect the dampner to the system, as close to the source of pulsation as possible, and begin the flow of system liquid at normal operating temperature. The dampner will soon probably stop dampning; this is because the system temperature will have raised the pre-fill pressure to greater than the pulsation pressure. In this condition, the cushion volume is effectively out of circuit. In other words, the “gas spring” is stronger than the system force against it.
iii. You may have to do this and live with pulsation for several minutes while the temperature of the metal diaphragm transfers the temperature to the pre-fill chamber (1). Measure the pipe system temperature, say with a “heat gun”, and compare with the temperature of the dampner body.
iv. Drain down any system liquid to atmospheric pressure, and vent off nitrogen down to 98% of (4).
v. By trial and error, you may have to reduce the nitrogen pressure still further to 95% of (4).
vi. Please do not decrease still further without reference back to the factory. If an increase in pulsation is experienced, by REDUCING the nitrogen pressure, this is an indication that you are driving the metal diaphragm against its gas side stroke limiting plate.
B. Where the full application parameters were disclosed to the dampner supplier before time of dampner selection, the deflection volume, from gas side to liquid side metal diaphragm stroke limiting plates, will have been chosen to be at least twice the pulse volume. The volume of the nitrogen cushion chamber will have been chosen to be a sufficient multiple of the pulse volume to produce the requested level of residual pulsation.
Only by working within these constraints discussed above can a reasonable diaphragm life and adequate pulsation deduction be achieved
NOTE: The Pre-fill norm for dampners of the elastomeric membrane, or PTFE plastomeric diaphragm types - “Pre-Fill to 80% of system liquid pressure” - is hardly if ever applicable to metal diaphragm dampners.
4. If In doubt, please call the manufacturing plant.
PulseGuard Pulsation Dampeners
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