W-PT Pull Test Bar

The Pull Test is the fastest way to verify the operation and specification compliance of MPI

Yokes. Western’s W-PT is designed for ease of use with AC Yokes (10 Pounds or 4.6Kg)

where just one Bar is required.

For Yokes using the DC Method, several Bars are conveniently stacked and fastened

together, as illustrated to the right. The requirements vary, depending on the Reference

Specifications. ASME Section V, Article 7 requires 40 Pounds or 18.2Kg. ASTM E709 and

E1444 require 30 Pounds for a Pole Spacing of up to 4” and 50 Pounds for a Pole Spacing

up 6”. All W-PT’s have Serial Numbers, and are supplied with Certificate of Compliance.

Testing of MPI Yokes is usually done with the Legs Straight for ease of the test. Leg Spacing

should have no effect on the Lifting Force of any Yoke (AC, AC/DC, 12Volt, Cordless,

or Permanent Magnet), as the losses in the Leg Hinges is the same if they are straight or

adjusted to 90 degrees. The one item that must me watched, when doing a pull test, is

that the Bottom of the Feet remain flat and in full contact with the Pull Test Bar. This may

require tightening of the Leg Hinges, or by cutting a small piece of wood (non-metallic)

to fit between the fully extended legs. However, the legs should be loosened when testing,

so the operator can be mindful of the ‘Contact’ with the workpiece.

Pull Testing is fast and easy with any AC Yoke, however operators must be mindful of Pole

Spacing with DC Yokes. Virtually all specifications limit Pole Spacing to 6” (150mm) with

a DC Yoke, for very good reason. As the poles of a DC yoke are moved apart the flow

of flux, from the positive pole to the negative pole, progressively reduces. When the poles

are spaced beyond this maximum distance the flux flow will stop, thus changing the field

characteristics drastically and not allowing indications to form.

The obvious items like; Condition of a Yoke’s Pole Pieces, Flatness of the Feet, and other

equipment serviceability issues must be adhered to. An item of greater importance in

testing the effectiveness of a Yoke (and its operator) is the use of some type of inspection

verification, such as a W-PT-DB, QQI’s, Castrol Strips, or a Pie Gauge, however nothing

beats a test coupon with an actual defect!

Every third party auditor will want to see current Certification for Pull Test Bars, and this

uneducated question leads inspection personnel too assume that a ‘Calibration’ should

be done annually, but this is not the case. ASTM E719, as well as ASME Section V,

Specifications state that a Pull Test Bar(s) only need to be recertified when there are

physical signs of damage which may affect the weight. Handling Scratches, dents, or

removal of the protective Conversion Coating will not affect the weight, however heavy

Scratches (Gouges) may be cause for concern. W-PT’s are manufactured to weight

10.1 Pounds or 4.7kg thus physical damage from normal use should not be a concern.