�ǳ�web Knowledgebase - fitting

The Importance of Zero Dead Volume Fittings

Rachel Desenberg — Thu, 14 May 2020 20:23:04 +0000

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Just as a chain is only as strong as its weakest link, a valve or system’s quality of operation is only as good as its connections—specifically, its fittings. This article will discuss what zero dead volume fittings are, explain why they are important, and provide specific examples of how they are used with two of �ǳ�web’s precision isolation valves.

What are ZDV fittings?

Dead volume is any space in the flow path that is not cleanly swept by the media’s laminar flow. Figure 1 (below, left) shows a cross section of a valve secured to a manifold. The media must flow from the valve, through the manifold, and into a fitting. The zone highlighted in red shows the dead volume. This is an extreme case and would not be used in applications where dead volumes severely reduce the quality of a system’s function. However, it demonstrates how hardware and channels drilled into manifolds add to the total volume a fluid must traverse, and how the fluid may not be able to cleanly sweep through.

Figure 1: Valve secured to a manifold with standard fitting

Figure 2: Example of a zero dead volume fitting
(Source: IDEX)

Zero dead volume (ZDV) fittings are special fittings which eliminate dead volume by ensuring the outlet seals right against the inlet that takes the medium out of the immediate system (or vice versa). These types of fittings typically include a nut and a ferrule that is inserted into a specially drilled hole. When correctly installed, the nut and ferrule allow the gripped tubing to seal directly onto the outlet surface, causing little to no disruption in laminar flow (Figure 2, above). Notice there is no gap between the tubing and the inlet’s surface where it must seal and that the tubing is flush against the surface. If there was a gap, a seal would not be guaranteed and the system would have added dead volume.

Why are ZDV fittings important?

Figure 3: Results with and without ZDV fittings
(Source: Chromservis)

Dead volume can lower the overall efficiency of a system by reducing response time and causing diffusion of the media (due to the disruption caused to flow). For certain applications, such as chromatography, dead volume is a great enemy that can skew results and even cause method transfers or system suitability testing to fail because it leads to too much diffusion (Figure 3, right). Limiting or eliminating dead volume is especially important in applications using expensive solvents or compounds that must go through the system. The smaller and more streamlined the internal volume, the better.

Just how critical a zero dead volume fitting is will depend on the specific requirements of the application. Is it important to use as little media as possible? Is cleanliness a priority? Does the system need to be fully flushable? Is the media sensitive to disturbances in the flow, i.e. diffusion? Is limiting dead volume imperative to getting reliable results? If the answer to any of these questions is yes, the application may benefit from a zero dead volume fitting.

Selecting an Appropriate ZDV Fitting

From stainless steel to plastic, there are hundreds of different types of fittings that can be used. Selecting the most appropriate fitting requires not just knowing what type of connector or fitting is needed, but also understanding various other aspects such as the size of the head of the fitting, the seal material, potential chemical compatibility issues, valve ports, depth of port, the maximum depth of the port’s threading, etc. However, when using a ZDV fitting in combination with a precision valve, the manufacturer of the valve should be able to recommend an appropriate fitting to help ensure maximum valve performance.

�ǳ�web has two high-precision isolation valves that warrant the use of zero dead volume fittings—the NIV series all-PTFE isolation valve, and the Eclipse proportional isolation valve. Both of these valves were designed to have the least amount of internal volume and minimal dead volume.

ZDV Fittings for �ǳ�web NIV Series PTFE Isolation Valves

�ǳ�web NIV series isolation valve ports are designed for flat-bottomed flanged or flangeless fitting. These are typically two- or three-piece fittings which are often referred to as compression fittings. On some low pressure valves, a barb style fitting may be used that would have the same features as the compression fitting by sealing on the bottom of the port. The flat bottom port enables the flange or ferrule to come in direct contact with the orifice of the valve, thereby eliminating any dead volume. This type of fitting is commonly used throughout the industry and is available from companies such as:

ZDV Fittings for �ǳ�web Eclipse Proportional Isolation Valves

Figure 4: Eclipse valve with ZDV fitting

The zero dead volume configurations (EIVU-Z, EIVU-Z-ENS) of the Eclipse valve use two zero dead volume fittings, each a nut ferrule combination that is a flangeless 1/4-28 flat-bottom fitting for 1/8" OD tubing. This fitting seals the tubing up against the underside of the ceramic that has an inlet and an outlet beneath a sliding channel that tightly controls flow (Figure 4, right). The recommended tubing for the Eclipse is Tefzel (ETFE) tubing, 1/8" OD x 1/16" ID. It is important that the tubing is stiff to allow the ferrule to grip it without causing it to collapse.

�ǳ�web Fittings: ZDVF-18
Recommended Bulk Fittings: XP-348
Recommended Tubing: 1530

Zero dead volume fittings (ZDV) are not always required, but they make a measureable difference when a system needs to be fully flushable or when dead volume is a severe detriment to its operations. For more information on internal volume and flushability, see Critical Aspects of a Valve's Internal Design.

By Jess Koeniguer • Design Engineer • �ǳ�web

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Eclipse Proportional Isolation Valve	NIV Series PTFE Isolation Valve	Zero Dead Volume Fittings

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Critical Aspects of a Valve's Internal Design

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Barb Fittings vs. Push-Quick Fittings

Rachel Desenberg — Thu, 29 Mar 2018 15:53:59 +0000

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Product Information

Should you use barb fittings or push-quick fittings for your application? If you're having trouble deciding, you're not alone. Here are a few things to consider when trying to decide which type of fittings are most appropriate for your application.

Push-Quick

Easier to disconnect
Better suited for applications which require frequent connecting/ disconnecting of hoses
Usually provide higher flows than equivalent barb fittings
Work best with stiffer tubing
Measured based on tubing outer diameter (O.D.)

Hose Barb

Tend to create a better seal
More difficult to disconnect
Better suited for "low-leak" environments/applications
Usually lower cost than equivalent push-quick fittings
Work best with softer tubing
Measured based on tubing inside diameter (I.D.)

Tubing Size

The first thing you should consider is your tubing size. Barb fittings are measured by tube I.D. (inner diameter), while push-quick fittings are measured by tube O.D. (outer diameter). If you already have tubing that you are using, be sure to match the tubing to the appropriate fitting for a tight seal.

Frequency

Next, consider how frequently you will be connecting hoses to the fittings. If you plan to disconnect and reconnect hoses frequently, then push-quick fittings will make this easier. If you plan to set up your system and leave the hoses attached for several years or longer, barb fittings might be a better option.

Durometer of Tubing

Finally, consider the durometer of your tubing. Barb fittings create a better seal on a slightly softer hose, while push-quick fittings are easier to use with stiffer hose. For example, �ǳ�web recommends using our 85A durometer polyurethane tubing for barb fittings, and 95A durometer polyurethane tubing for push-quick fittings.

Refer to the charts below for a comparison of flow rates or to view �ǳ�web's tubing recommendations. Still have questions? Click here to contact us for additional assistance.

Recommended Tubing Specifications
	Polyurethane	Polyethylene	Polypropylene	Nylon

Durometer	Shore A85 or higher	Shore D44 or higher	Shore D44 or higher	Shore D44

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�ǳ�web Push-Quick Fittings Adapters & Plugs

Chris Agricola — Wed, 09 Jan 2013 18:30:35 +0000

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Product Tips

�ǳ�web offers a variety of accessories that are designed for use with Push-Quick Fittings. These include special #10-32 threaded adapters in both male (p/n 11674) and female (p/n 11675) thread configurations and adapters that can be used to plug a Push-Quick fitting.

The threaded adapters insert into Push-Quick Fittings and provide either a male or female thread that can be used to mount any �ǳ�web product with a #10-32 threaded inlet. This allows the direct attachment of the product to a Push-Quick Fitting without hoses or additional fittings.

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Push-Quick Plugs
�ǳ�web offers a variety of Push-Quick Plugs in sizes to fit 1/8” through 3/8” O.D, tubing. These plastic plugs may be used to plug the port of a Push-Quick Fitting for later use. Used as a temporary plug, they may later be removed and tubing inserted to connect to an additional line of a circuit.

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�ǳ�web Push Quick Fittings Installation & Removal Instructions

Chris Agricola — Thu, 20 Sep 2012 20:23:07 +0000

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Installation Instructions

Installation of Tubing or Hose into fitting
1. Slowly push a clean and perpendicularly cut tubing into the fitting until it comes to a dead stop.
2. Pull the tubing back gently until the Gripper Ring of the fitting grips onto the tubing and has a good seal.

Removal of Tubing of Hose from fitting
1. Push in evenly on the two long oval sides of the Release Button.
2. Pull out the tubing while keeping the Release Button depressed.
3. To reuse the tubing; cut off the lodged portion of the previously used tubing evenly and perpendicularly.

Installation of Pipe Fittings with Pre-Applied sealant
1. Tighten fitting by hand, then turn it 2 or 3 turns with a wrench until it reaches the desired torque listed.
2. If the fitting is used and the sealant coating is not in good condition, apply Teflon® sealant tape to the threads.

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�ǳ�web Single-Barb Pneumatic Fittings

Chris Agricola — Thu, 20 Sep 2012 17:33:22 +0000

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Product Tips

�ǳ�web Single-Barb Fittings

• Allow for easier assembly onto tubing
• Provide less leakage potential and increased pressure performance
• Reduce the need to constantly tighten the assembly
• Provide a single sharp edge allowing the barb to catch onto the tubing for a leak-free connection
• Require less clamp pressure
• Allow tubing to “relax” to its original size which is essential to the assembly and pressure of the connection.

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Tips on Using Hose Barb Fittings

Chris Agricola — Thu, 20 Sep 2012 17:28:34 +0000

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Product Tips

Hose or Tubing Size. The use of different sizes of hose or tubing in your circuits deserves some care and consideration. In general, follow the manufacturer’s guide for the size of hose or tubing you use. For air logic circuits, we recommend 1/16” ID for pilots and 1/8” ID for supplies and outputs.

Swivel Fittings. Minimatic® swivel connector fittings are very efficient in applications where joints need to be disconnected and reconnected frequently. Made with a threaded connection on one end and a swivel connection on the other, these fittings provide a true cost savings on pneumatic circuit designs. They are valuable also where short lengths of hose are being connected. Note: These are not rotating joints. They are for assembly benefits . . . not as a constant rotation connection.

Tightening #10-32 Fittings. TIGHTEN WITH CARE. Often a “finger tight” connection between �ǳ�web fittings with anaerobic sealant is all that is required. When using a gasket, most �ǳ�web #10-32 threaded fittings require no more than 9 inch-pounds of torque to seal. We recommend that this force not be exceeded. Use wrench #11770 with a 1/4” and 5/16” open-end.

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