6.2 Type B Meter Equipment, Calibration, and Setup
Key Takeaways
- A Type B meter has a bowl of at least 0.075 ft³ (about 2.0 L) capacity, a cover with an integral air chamber and hand pump, a pressure gauge graduated to read air directly, two petcocks, a main air valve, gasket, and clamps.
- The dial is graduated to read air content to the nearest 0.1 percent, and the calibration must be checked at intervals not exceeding three months and whenever results are questionable.
- A leak at the gasket, rim, clamps, petcocks, or air valve drifts the reading and invalidates the test even when the sample is good.
- Type B differs from Type A: Type B equalizes pressure from a pre-pressurized air chamber into the bowl, while Type A observes a water-column drop under applied pressure.
Anatomy Of A Type B Meter
The Type B pressure meter is a measuring instrument, not just a pot with a gauge. Its parts each do a job because the method depends on a sealed pressure system:
- Measuring bowl: a flanged cylindrical container of known volume, at least 0.075 ft³ (about 2.0 L) capacity, with a machined rim that mates to the cover gasket.
- Cover assembly: contains an integral air chamber, a hand air pump, the pressure gauge, the main air valve between the chamber and the bowl, two petcocks for water and venting, and a bleeder/pressure-release path.
- Gasket and clamps: seal the cover to the bowl rim and hold it down evenly.
- Pressure gauge: graduated to read air content directly to the nearest 0.1 percent.
A standard tamping rod (5/8 in / 16 mm diameter, about 24 in long, with a hemispherically rounded end), a rubber mallet, a strike-off bar or plate, and a means to inject water through a petcock (bulb syringe or wash bottle) round out the kit.
Each part exists because the method is a sealed pressure system: the bowl fixes the concrete volume, the cover stores pressure, the petcocks pass water and vent air, the main air valve gates the equalization, and the gauge translates the response into percent air.
Type B Versus Type A
Both meters are pressure meters, but they read differently. The exam may ask you to tell them apart.
| Feature | Type A | Type B |
|---|---|---|
| Reading principle | Water-column drop under applied pressure | Pressure equalization from air chamber into bowl |
| What you watch | Water level falls in a graduated tube/cover | Dial gauge needle settles to a percent-air value |
| Pressure source | External pump or squeeze bulb over water | Built-in hand pump charges an internal air chamber |
| Common use | Less common today | Most common field meter |
| Reading | Computed from water-column drop and gauge pressure | Direct percent air on the dial |
In a Type B test you pre-pressurize the air chamber to an initial pressure line, then open the main air valve so that chamber pressure equalizes into the air voids in the bowl. The needle settles on the apparent air percent. In a Type A test you fill the cover with water and read how far the water column drops when a set pressure is applied. Both still require the aggregate correction factor.
Calibration And Leak Control
Calibration is the first equipment concept. The bowl volume must be known and the gauge must read true percent air. The standard requires the calibration (the test to check the air-content graduations) to be performed as often as necessary and at intervals not exceeding three months, and again whenever results become questionable or the meter is dropped, repaired, or shows a gauge that will not return to zero. A field technician need not run a full calibration before every test, but is responsible for refusing a meter that is out of calibration or unreadable.
Leak resistance matters just as much. A cut or paste-clogged gasket, a dirty rim, loose or uneven clamps, a sticking air valve, or a clogged petcock all let pressure escape, which drifts the apparent reading. The same risk appears if the gauge will not hold the initial pressure line.
| Component | Pre-test check | Failure effect |
|---|---|---|
| Bowl | Clean, correct volume, undamaged rim | Wrong volume / poor seal |
| Gasket & rim | Seated, uncut, paste-free | Pressure leak |
| Clamps | Tight and even | Cover lifts, leaks |
| Petcocks | Open, clear, controllable | Cannot vent or add water |
| Air valve & pump | Holds initial pressure line | Bad equalization, false air |
| Gauge | Returns to zero, readable to 0.1% | Misread air content |
The right response to a leaking, sticking, or out-of-zero meter is to correct or replace the equipment before testing, never to average a suspicious reading or report a number from a meter known to be unreliable.
Setup Discipline Before The Timed Sequence
Good C231 work looks calm because the preparation is finished before the clock starts. Set the meter on a stable, level surface so that filling, rodding, tapping, strike-off, clamping, pumping, and reading can all happen without the meter tipping or picking up vibration from nearby work, which can shift the needle. Keep the sample shaded and covered nearby, have water and the injection bulb ready, and confirm the gauge returns to zero with the cover off and no pressure applied.
Cleaning is a measurement control, not housekeeping. Hardened mortar inside the bowl changes its volume; paste on the flange holds the gasket open; sand in a petcock blocks venting; a filmed gauge face causes parallax misreads. Because pressure testing is sensitive to small leaks and small volume errors, these details directly change the number.
Setup sequence:
- Confirm the meter is in calibration and appropriate for the aggregate.
- Inspect bowl, rim, cover, gasket, clamps, petcocks, valve, pump, and gauge.
- Clean every surface that affects volume or sealing.
- Verify the gauge zeros and the pump holds the initial pressure line.
- Stage water, the injection bulb, rod, and mallet within reach.
- Place the meter where it can stay level and undisturbed.
Reject any meter that leaks, sticks, will not zero, or has an uncertain bowl volume. Equipment readiness is the technician's first defense against an invalid air content.
What is the maximum interval allowed between calibration checks of the air-content graduations on a C231 meter?
Which statement correctly distinguishes a Type B meter from a Type A meter?
To what precision is the Type B pressure gauge graduated to read air content?