As fluid moves through a Viking gear pump – from the suction port to the discharge port – it’s natural for a small amount of fluid to seep through internal clearances to the backside of the rotor. In most applications, this isn’t a problem. But in others, this pressurized slow moving fluid can cause some rather annoying issues. Today we’re discussing something known as a suckback and how it can help a gear pump.

Typically, the path of the slipped fluid is simple – a small amount of fluid slips through internal clearances at the discharge port and collects behind the rotor. It then travels behind the rotor to the suction side of the Viking gear pump, where it again makes its way through internal clearances and back into the pump.

This process goes largely unnoticed in many circumstances, but there are some scenarios where this small amount of slip can be a real problem. Here are some examples.

Chocolate (And Other Temperature Sensitive Fluids): Chocolate is one of the most difficult fluids to pump, so naturally it makes the top of this list. Because the fluid moves slowly behind the rotor, it sometimes has the opportunity to solidify and stall the pump. This is also true for other fluids that thicken or harden as they cool, such as corn syrups, adhesives, resins, etc.

Packed Pumps and Thin Fluids: When a packed Viking gear pump that is handling relatively thin liquid is dealing with slip, you can just about guarantee you’ll have excessive leakage through the gland. Because the slip behind the rotor is under pressure, the fluid seeks the path of least resistance. In this case, out through the packing gland.

Mechanical Seal Issues: It’s not just packing that has potential to slip through. Mechanical seals will do the same if they are having issues due to heat buildup, liquid stagnation, accumulation of abrasives, or any other multitude of circumstances that cause mechanical seals to leak.

Reduce or Eliminate Slip Issues With a Suckback

A suckback is a hole drilled in the casing from the suction port to the area behind the rotor. Its function is to promote additional flow through the area by reducing pressure. Specifying a suckback on a new pump (or installing one on your current pump) helps keep fluid moving so it has less opportunity to set up or harden.

If you think your pump needs a suckback, do NOT make your own. Consult an engineer first to make sure this alteration is right for your application, and trust the modification to the manufacturer or service shop that is authorized by the manufacturer.

If you have questions regarding your Viking gear pump, call us today – we can answer all your questions.

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