Rod Pumps and Accessories for Gas Locking and Gas Handling Conditions

Variable Slippage Pump® (VSP)

  • Eliminates gas locking, fluid pound and gas pound
  • Adjustable slippage to match needed gas handling
  • Easy to adjust by raising or lowering polished-rod clamp
  • Increased minimum polished-rod load for greater sucker-rod life
  • Corrosion- and abrasion-resistant materials available

The patented Variable Slippage Pump® is a sucker-rod-drawn, positive-displacement pump which operates on the principle of pressure equalization just before the plunger reaches the top of the upstroke.

Existing pump designs rely on the ability of the pump to produce high pressure in the compression chamber during the downstroke. This high pressure is needed to open the traveling valve and allow fluid and gas to flow through the plunger for lifting to the surface on the upstroke. Failure of the traveling valve to open on the downstroke in gassy wells causes a gas-locked condition and no production.

The VSP® has a gradual taper in the upper barrel. As the plunger enters this taper near the top of the upstroke, slippage increases past the plunger, and pressure is equalized above and below the plunger and traveling valve. Therefore, when the plunger starts downward, the traveling valve opens easily since high pressure in the compression chamber has already been achieved.

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Two Stage Hollow Valve Rod Pump

This pump has become the most popular pump design invented by Harbison-Fischer. It is a rugged pump which overcomes most gas locking conditions and has the ability to produce a moderate quantity of sand or other particulates. The secret to the success of the Two Stage Hollow Valve Rod Pump is its modified upper compression chamber.

At the beginning of the downstroke, the upper traveling valve on top of the pull tube holds back the hydrostatic head and allows the lower traveling valve to open without the need to compress the fluid/gas mixture to a high pressure. As the downstroke continues, the fluid/gas mixture from the lower compression chamber moves through the plunger to the upper compression chamber.

At the start of the upstroke, the lower traveling valve closes and the standing valve opens to admit new fluid to the lower compression chamber. During the upstroke, the fluid/gas mixture in the upper compression chamber is compressed to a higher pressure until the top traveling valve opens and allows the fluid to be discharged into the tubing above the pump completing the pumping cycle.

The valve rod guide has a generous clearance to allow sand and other particulates to be flushed from the upper compression chamber during the upstroke. This characteristic gives the Two Stage Hollow Valve Rod Pump its versatility in gas locking applications which also produce sand or other particulates.

The Two Stage Hollow Valve Rod Pump is available in a wide variety of materials, surface treatments and configurations. The configurations use mainly stock parts to create this special pump.

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Gas Chaser Pump


The Harbison-Fischer Gas Chaser Pump is designed for the very worst gas locking problems that are encountered in rod pumped wells. It is similar in design and theory of operation to the Two Stage Hollow Valve Rod Pump and achieves a higher compression ratio by using an absolute seal at the top of the upper compression chamber.

The Harbison-Fischer Gas Chaser Pump transfers the fluid/gas mixture to the upper compression chamber on the downstroke and produces this fluid through the hollow upper plunger on the upstroke. The highest compression ratio is achieved by spacing the pump from the top. It is available in several materials as well as thin wall and heavy wall configurations for shallow or deep wells.

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Loc-No® Plunger

The Harbison-Fischer Loc-No® Plunger is an established tool in the Harbison-Fischer arsenal of gas lock fighting solutions. It was designed to provide a mechanically opening traveling valve in order to overcome the need for high compression in the pump compression chamber.

The plunger is assembled with a hollow plunger sleeve, a center connecting rod, an upper connector and a lower drop to seal against the bottom of the sleeve on each upstroke of the pump. The drop and sleeve are inlaid with a hard Stellite lining that resists wear and corrosion.

The Loc-No® Plunger has two influences that help it open on the downstroke without relying on pump compression. The movement of the plunger rod is pushing the drop away from the plunger sleeve and the friction between the plunger sleeve and the inside of the barrel tube causes the plunger sleeve to resist downward movement. When the drop moves away from the plunger sleeve the fluid/gas mixture is free to flow up through the plunger as it falls through the fluid gas mixture. On the upstroke, the sleeve seals against the drop and lifts the fluid/gas toward the surface.

The Harbison-Fischer Loc-No® Plunger is a proven product that is an inexpensive replacement for the plunger, plunger coupling, traveling valve and seat plug in a standard pump.

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Sliding Top Valve

The Harbison-Fischer Sliding Top Valve is an elegant solution to the problem of gas locking and is helpful in fluid pound conditions. It has a free-floating, hard bronze sleeve that rides up and down on the valve rod in a steel housing.

On the pumping downstroke, the sleeve follows the valve rod down and seals off the hydrostatic pressure from above by shutting off the fluid flow passages through the housing. This simple action removes the hydrostatic pressure load from the traveling valve and allows it to open at the beginning of the downstroke without the need to build up a high pressure in the compression chamber. As with the Two Stage Hollow Valve Rod Pump and Gas Chaser Pump, the fluid/gas mixture moves to the area above the plunger.

On the upstroke, this fluid/gas mixture above the plunger is compressed until the sliding sleeve in the Sliding Top Valve opens and allows the fluid to be discharged into the production tubing above the pump.

The Sliding Top Valve is also useful to cushion fluid pound. A part of the downward force that causes the destruction associated with fluid pound is the hydrostatic pressure above the plunger acting on part of the plunger area. The Sliding Top Valve holds back this hydrostatic head and thus reduces the load on the plunger when it contacts the fluid.

It is available for all sizes of insert and tubing pumps. The bronze sliding sleeve is available with an abrasion resistant coating when particulates are produced.

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Travel No-Loc Valve

The Harbison-Fischer Travel No-Loc Valve is an adaptation of the Harbison-Fischer Loc-No® Plunger concept to a Traveling Barrel Pump design. This device gives the Traveling Barrel Pump an opportunity to work without gas locking while retaining all of the advantages of a common Traveling Barrel Pump. The seal faces on the Travel No-Loc Valve are hard Stellite inlaid to prevent wear and corrosion.

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