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Liquid-filled vs. Direct Drive Pressure Gauges vs. PLUS! Performance

pressure gauge | direct drive gauge | liquid filled gauge

Your application requires specialized pressure measuring equipment that has the proper accuracy, safety and quality features you need. If your application involves excessive pulsation and/or vibration you need to take measures to protect your pressure gauge from damage.

There are many options for pressure gauges out there today that ease the effects of pulsation and vibration, so how do you know which one is right for your process?

Liquid-filled pressure gauges, direct drive pressure gauges and Ashcroft’s PLUS!™ Performance option each have their own pros and cons to consider.

This article will describe each pressure gauge option and why you might consider them (or not consider them) for your application.

What is a Direct Drive Pressure Gauge?

Direct drive gauges are typically used for severe shock and vibration applications. They feature a movementless design, which eliminates movement wear under high vibration process conditions.

Direct drive gauges are without a movement, meaning there is only one moving part, the bourdon tube making them an alternative to conventional bourdon tube gauges with a movement when severe vibration and shock are concerns. These gauges are composed of a helically wound bourdon tube attached directly to the pointer shaft.

Direct Drive Gauge Pros

Here are some pros of direct drive gauges:

  • Dampens effects of vibration and shock
  • Liquid filling gauge case not required with direct drive design
  • Fewer moving parts to wear out
  • Steady pointer under harsh process conditions
  • Available with mini seals (like the Ashcroft 310)

Direct Drive Gauge Cons

Some of the cons of this type of gauge include:

  • Higher cost than conventional bourdon tube gauges
  • Risk of clogging with dirty process media
  • Only available with Inconel bourdon tube, which may not be compatible with some process medias
  • Gauge difficult to recalibrate

What is a Liquid-Filled Pressure Gauge?

As you might know from the name, a liquid-filled pressure gauge is a pressure gauge that’s filled with a liquid like silicone or glycerin. This improves its performance in harsh conditions, including those with, pulsation and vibration.

Liquid-Filled Gauge Pros

The pros of liquid-fill include:

  • Dampens effects of pulsation/vibration
  • Keeps moisture out of case and condensation off window, typically IP65/66
  • Lubricates internal mechanical components
  • Variety of manufacturers for more availability
  • A throttle screw is typically standard to fight the effects of pulsation
  • Best option for extremely severe applications

Liquid-Filled Gauge Cons

The cons of liquid-fill include:

  • Potential for leaking
  • Gauge fill needs to be removed before recalibrating zero and span
  • Potential for freezing in low ambient temperature conditions
  • Potential for fill discoloration
  • High cost for inert liquid fills like Halocarbon or Flurolube required for oxygen service or other oxidizing media

What is Ashcroft’s PLUS!™ Performance?

PLUS!™ Performance is a dry case pressure gauge that dampens pulsation and vibration and improves gauge readability without the headaches of a liquid-filled gauge.

This proprietary Engineered Dampening Media (EDM) of a gauge with the PLUS!™ Performance option is injected into a canister that surrounds the gauge movement pinion shaft, movement plate, and backplate. The movement technology, or PLUS!™ Performance, utilizes a thixotropic liquid that adheres to the pinion.

As gauge pressure increases or decreases, movement of the gauge pinion creates shear load, which causes EDM molecules to scatter. The EDM material gets thinner at the layer being sheared. With applications involving vibration, this allows dampening of the gauge pointer. This action allows for a steady, flutter-free pointer.

PLUS!™ Performance Pros

This option has some advantages over standard dry or liquid-filled gauges:

  • Dampens effects of pulsation/vibration
  • No leaking concerns
  • Safe for applications with oxidizing media at a considerably lower cost
  • Lower cost than a liquid filled or direct drive gauge
  • More eco-friendly disposal
  • No fill lines like those associated with liquid-filled gauges
  • Easier to recalibrate than a liquid-filled gauge (no leaky mess)
  • Wider ambient temperature range than glycerin
  • Can reduce inventory by not having to stock both dry and liquid-filled gauges
  • Works well with diaphragm seals

PLUS!™ Performance Cons

The cons include:

  • Does not protect against water ingress
  • Does not keep condensation off the window (but if you require IP65/66, you can order either the hermetically sealed version or the new X1P to meet specifications if there is a condensation issue)

You can learn more about PLUS!™ Performance on in our brochure.

We don’t like to pressure you, but we have more information.

Now that you understand the difference between liquid-filled pressure gauges, direct drive pressure gauges and Ashcroft’s PLUS!™ Performance, you can choose the solution that’s right for your application.    

If you want to learn more about pressure gauges, here are a few related articles to check out:

Feel free to contact us today to talk to one of our industry experts and get your questions answered.

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About John Girard, Product Marketing Leader

John Girard is currently the Product Marketing Leader for Diaphragm seals at Ashcroft. Formerly, he was the Territory Sales Manager responsible for supporting the distribution network in the Northeast. He began with Ashcroft as a Product Specialist for mechanical pressure gauges and accessories. He transitioned to a Sales Engineer role working with engineering firms on specifications. John achieved an M.B.A from Johnson & Wales University and has 10+ years of experience working with Sales and Marketing.