Test Valve - an overview

6.3.2.2.2 The traveling valve test

The traveling valve test (TV test) checks, with the same arrangement as used in the standing valve test, whether the traveling valve and/or the barrel–plunger fit is leaking. The pumping unit is gently stopped on the upstroke of the polished rod, near the top of the stroke. As the polished rod comes to a stop, the load on the dynamometer is immediately recorded. At this moment, the status of the pump valves is as shown in Fig. 6.16: the traveling valve is closed and the standing valve is open. The initial polished rod load, as recorded, represents the sum of the rod string weight in well fluids and the fluid load acting on the plunger. The standing valve is considered to be open and carries no load. If a perfect seal between the traveling valve seat and ball, and additionally, a perfect fit of the pump barrel and plunger, are assumed, then no change in polished rod load with time should occur. This condition is checked, as in the SV test, by pulling the cord of the dynamometer at several times in order to record the change in polished rod loads.

Any leakage in the traveling valve or between a worn pump barrel and plunger permits fluids to pass from above the traveling valve. This fluid leakage will slowly increase the pressure in the space between the pump's two valves, and the standing valve is slowly forced to close. As soon as it closes, the fluid load is no longer carried by the plunger and the rod string, but it is completely transferred to the standing valve and the tubing. The process of load transfer can be observed at the surface where polished rod loads are recorded on the dynamometer card at regular intervals. The original polished rod load, representing rod string weight plus fluid load, as recorded on the card (the long horizontal line on the example card in Fig. 6.16), is always greater than the loads measured later on. The rate of load decrease is, again, directly proportional to the leakage rates.

It should be clear from the above discussion that a TV test cannot differentiate between the effects of a leaking traveling valve and the leakage in the pump due to a worn barrel or plunger. As a rule, a measured loss in polished rod loads in about 5 s is a positive indication of traveling valve leaks and/or an increased slippage past the plunger. As is the case with SV tests, the traveling valve test should also be repeated at different points in the upstroke. Differences in load loss rates observed during subsequent tests can indicate uneven wear or the position of a split in the pump barrel.