The operation and longevity of air operated diaphragm pumps are often affected by the style and operation of the pump unit.
When purchasing a diaphragm pump unit, consideration needs to be given to the way this unit will be operated in order to not only enjoy a troublefree ongoing operation without continual stoppage and downtime frustrations, more importantly, to protect the operating budget.
Maintenence/ repairs and the associated costs can be greatly reduced by the correct installation of auxiliary components that support the actual pump unit.
Double diaphragm pumps by their very design, transfer fluid from the diaphragm chamber by exerting air pressure on the air side of the diaphragm which is greater than the pressure the fluid side will exert on the diaphragm. The higher pressure on the air side caused the diaphragm to expand into the fluid chamber, thus the diaphragm forces the fluid out of the liquid side of the pump chamber.
In a fixed installation, the liquid pressure is relatively fixed, in other words, pipe lengths are stable, filters, heater or cooling coils, valves and other fluid side losses remain relatively constant. This also means the air pressure regulator can be fixed and left at a specific setting. In other words, the air pressure is fixed and balanced to generate a specific force on the diaphragm which will generate the pump flow rate required by the system.
Every time the pump starts, it starts against a fluid side of the diaphragm which is full of liquid with a known pressure. The pump produces the required flow based on the air pressure as set on the air pressure regulator when commissioning the system.
The operator or plant automation simply turn on the air side valve or the fluid side valve to start or stop the pump. There is no need to reconsider the pump system as it is a static installation. The only time this changes is when the discharge pipework is cleared, emptied for or when a new component needs to be installed. This is the added challenge to operating air diaphragm pumps in a mobile installation.
A mobile installation, however, requires an operator that understands that the pump, having been moved from the store or another location on the plant to this new pump position, will now start with an empty pump chamber. An empty suction hose or pipe (in a self-priming situation) and an empty discharge line. If there is a filter regulator attached to this pump, it is likely that the regulator will have the setting of the previous pumping position. It may be as high as plant pressure up to 8 bar.
Imagine what happens when the plant air is applied for the first time to this diaphragm. Zero fluid in the fluid side of the chamber to counter the 8 bar on the air side. The result is that the diaphragm goes into overdrive, “searching” for a balance to the air side pressure. One will often hear the pump cycling (oscillating from one side to the other) at a fast pulse rate until fluid enters the chamber and the discharge line begins to fill. As the line fills, pressure begins to equalise and the pump slows to a more steady pace. If the diaphragm installed is Teflon, it is very likely to already have stretched and possibly even cracked or in other ways been damaged by this action.
The two installations, fixed or mobile, while similar, need a very different operator and management. The auxiliary equipment fitted needs to be the same for both installations, however, the operator needs to be trained and far more aware of the “commissioning” of this pump in its new position.
Basic auxiliary equipment:-
- A baseplate or wheeled trolley.
- An air filter regulator.
- A fluid side suction strainer. (if required to protect the pump from debris)
Correct commissioning of a diaphragm pump from an air pressure point of view.
- Adjust the plant pressure at or as close to the pump as possible with the individually installed air filter/regulator to around 2,5 Bar.
- Turn on the plant air to the pump slowly adjusting the volume of air with the air valve so that the pump cycles at around 60 to 70 beats per minute.
- If the pump starts to slow, slowly open the valve for the plant air line.
- If the pump is still slower than 60 to 70 “beats” per minute slowly open the air pressure regulator to increase the air pressure onto the diaphragms.
- As the pump fills the discharge line and starts to take up the back pressure in the pipeline, the balance pressure demand on the diaphragms will increase.
- Once the pump is cycling at 60 to 70 cycles per minute, stop increasing the air pressure and lock the filter/regulator in place, (normally pushing down on the adjustment cover)
The above commissioning is normally only done once in a fixed installation, however, in a mobile operation where pumps are moved from application to application, this procedure needs to be done every time the pump is moved and started.