Sunday, January 13, 2013



Wilden or Versa-matic diaphragm pumps need no special introduction. These are air operated diaphragm pumps.

This piece is meant to highlight the safety and chemical resistance aspects. In any case every crew member must be familiar in rigging up a wilden pump as they are used for chemical spill contingency.

Wilden pump is not a submersible pump. You have to keep the pump just above the level of the liquid to be pumped.

There must be an awareness of the diaphragm material or the pump is spoilt and worse people could get injured very badly or there could be an explosion. It may develop fluid dischg pressure equal to the air supply pressure. Always wear eye protection when working with the pump.

See video below to understand how the pump works.

On chemical tankers we do not use neoprene or Buna rubber diaphragm wilden pumps. Rather only Teflon or Viton pumps are used . SS shell is preferred as many chemicals react with aluminium and alloys shells. 

Usual models supplied on board are M1, M2 and M4 models.  An M4 SS model with Teflon diaphragm will weigh about 19 kgs.

Teflon elastomeric diaphragms are not as efficient as rubber as the discharge capacity is reduced by 20% and the suction lift is also reduced. The wilden pump in the ballast pumproom can have a neoprene diaphragm.

If the chemical is viscous a larger non collapsible and reinforced inlet pipe is required to avoid cavitation. It is critical that on the suction side there must not be any leaks . The suction flexible mouth must be sliced off at an angle to mate on to the tank bottom.  

M2 pumps are used to mop the couple of litres of condensed water at the Framo deepwell pump suction mouths of all cargo tanks after final steaming.

Drain the compressed air line before you use it to power the wilden pump. This is most important if you are using it to pump a water reactive chemical. Imagine heat and exothermic sputtering of Sulphuric acid inside the pump because of a leaky diaphragm. 

If there are air bubbles in the discharge of the pump it means the diaphragm is torn or the diaphragm plated to pump shaft is not tight. Do not put your face next to the air exhaust which may be contaminated .

The bottom orifice is always the suction and the top one is always the discharge.

Always keep sufficient wilden pump spares.

If you have to use it inside the tanks use an air exhaust muffler—or you may land up wearing ear protection which is not desired.  Always shut off the air supply and disconnect it from the pump before doing any maintenance or inspection.

When pumping flammable and static accumulator liquids the wilden pump must be earthed. Sparks can ignite and cause an explosion. Many of you must have experienced wilden pump shock.

Never exceed the max temp limit of the diaphragm, balls and seats of your pump.
Viton/ -40C to 176 C
Teflon/ 4C to 105 C
Neoprene / -18C to 93C

( 30 Years in command.)


  1. Sir,

    Are the strokes in these kind of pumps fast enough to give a steady flow of fluid or the flow keeps pulsing ? Also how many strokes per minute a Wilden pump is capable of, depending upon the type of diaphragm used.


    1. hi matt,

      M2 will give 2 cubic metres discharge per hour, if you run the pump optimum.

      air flow can be controlled to decrease output.

      M4 will give 4 cum/ hour and so on.

      the flow is NOT steady like that of a gear pump or screw pump.

      capt ajit vadakayil

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