Rheonics SRV - X2 Custom Flange Viscometer

What products are involved?
SRV - Inline Viscosity Meter
What is the purpose of this article?
To give an overview of the SRV with Flange/Custom adapter connection (SRV X2), installation guidelines, instructions and special considerations. Flange norm, size, pressure rating, etc. should be defined by the customer with the order.

1. Introduction

SRV is Rheonics sensor for inline viscosity measurement (viscometer). Read more on SRV here.

This sensor configuration (SRV-X2) allows the client to determine the type of flange/adapter needed in case none of the other standard connections are suitable. There are very few limitations to what kind of process connection can be used, but it must follow the next considerations:

  • Flange material must be 316L or 304.
  • Flange/adapter thickness must be less than 1”.
  • Flange/adapter diamenter should at least have a 33mm size.
  • The flange connection on the line (customer interface) must have an inner diameter bigger than 26mm for the SRV sensor to fit.

When ordering this option, the customer needs to provide the norm, size and pressure rating of the connection. Either state this via text or attach a drawing of the flange. Because this is a custom build, the lead times are typically around 6-8 weeks.

Consider that even though large flange sizes are possible to mount, these rarely make sense from a process integration perspective. Large flanges tend to have large standpipes on the process side. This means that there is a potential risk of a stagnation zone. With the SRV flange, the extension into the fluid is limited to about around 80 mm. In case longer extensions are needed, you will need an SRV FPC - Long insertion sensor (SRV-X5).

Figure 1: SRV custom flange dimensions.


Rheonics SRV 

Order code
Connection type
Customizable flange/adapter
Drawing and CAD file


2. General installation guidelines

SR-sensors can be placed at any point in a process and at any orientation but is helpful to consider some terms that are usually involved in the sensor measurements.

2.1 Submersion

The viscometer SRV has a sensing element shown inside the red section in Figure 2. This section of the sensor should always be fully submerged in the fluid since SRV measures what is in contact with its sensing element. Incomplete submersion can be a problem when the flow rate is low and the pipe isn’t full. A possible solution for low flow rates is placing the sensor horizontally and parallel to the fluid (e.g. in an elbow) instead of a vertical and perpendicular installation. 

Figure 2: SRV sensing area

2.2 Stagnation/dead zone

Also is not good practice to have dead or stagnations zones around the sensing area (Figure 2). A stagnation or dead zone is where a fluid transfer is not good and older fluid may not be fully displaced by newer fluid. This leads to incorrect measurements due to part or all of the measurement being influenced by stationary fluid that is no longer representative of the actual process fluid. This is a clear consequence of long standpipes, once again, if the standpipe can’t be short enough, the client should use an FPC version of the sensor so the insertion depth can be modified.

A clearance of at least 5mm is also recommended between the sensor tip and a pipe wall or any other obstruction.

2.3 Orientation independence

SRV has a symmetrical tip, making it possible to face a flowing fluid in any direction. Its shape enables the fluid to be in contact with the tip without creating recirculation zones.

Figure 3: SRV sensing tip.

2.4 Flow

For Newtonian fluids flow rate does not affect the viscosity, so SRV should measure the same values in static and moving states of a fluid. For non-Newtonian fluids, the flow rate does matter and viscosity readings may differ between static and moving conditions. The recommendation for processes with non-constant flow rates is to install the SRV in a section in the pipeline with the most consistent flow rate to have a steady viscosity value.

Flow rate is also relevant to ensure the full submersion of the SRV sensing element into the fluid. For a process with a low flow rate, pipes may not be full of fluid at all points, so SRV should then be placed in a section where the pipe is usually full of fluid (i.e. after a pump).

In all cases, the SRV’s sensing element should be completely submerged in the fluid. It’s best to avoid installations with long standpipes, since that may lead to a bad fluid transfer resulting in measurements that do not reflect the true state of fluid or worse high noise measurements.

When installing in a standpipe, choose the appropriate insertion length of the sensor by selecting long insertion probes. This allows the sensing element to clear the stagnation zone and be in the fluid that is of interest for measurement, as in the next figure.

Figure 4: Long insertion probes for long standpipes.

2.5 Fluid types

The SRV in general works well with almost all fluids as long as the installation is correct. Some common fluid types and scenarios are mentioned next: 

  • Static and moving Newtonian fluids
  • Moving non-Newtonian fluids (Viscosity can vary at different flow rates)
  • Inks
  • Blubbly fluids under moving conditions
  • Fluids with solids of micrometers scale

3. Process connection installation instructions

Since this sensor configuration (SRV-X2) has a custom flange, installation instructions can vary but the next steps are for a standard flange (eg. ANSI 150lb 2” RF).

3.1 Connection steps

A standard flange installation will require two flanges, a gasket in between, a bolt, two washers and insulating sleeves (for the bolt) for each hole on the flange.

Figure 5: Standard flange connection components.

i. Place the isolating sleeves, washers and bolts in each hole of one of the flanges (e.g. the process flange).

ii. Place the gasket, aligning it with the flange. Gasket type changes with flange norm and design.

iii. Insert the sensor with flange connection.

iv. Place the isolating sleeves, washers and nuts in the missing flange.

v. Ensure the gasket is still well placed and start bolting down the flanges. Consider tightening the nuts in a cross sequence.

 3.2 Specific Process Connection installation instructions

  • In line: For inline installations consider the sensing area (Figure 2) and a minimum clearance of the sensor tip to the pipe inner wall (5 mm). For most 1”, 1.5” or 2” pipes (for 2” it depends on the pipe norm) a perpendicular installation with the SRV correctly submerged is not possible. In those cases, the installation is recommended to be parallel as in figure 7.a. For lines bigger than 2” (figure 7.b), the sensor can be mounted perpendicular to the flow as long as the standpipe allows the sensing element to be submerged in flowing fluid. If the standpipe can’t be reduced (figure 7.c), the SRV FPC is recommended with a customizable insertion depth. The SRV Hygienic FPC is an alternative that creates a smoother variation in cross-section than the standard FPC.
  • In tank: Place the sensor at the bottom, wall or lid of the tank as long as the sensing element can be fully submerged in the fluid and dead zones are avoided. Usually, it is useful if the sensor is placed at a tank’s height that has always fluid.
  • Others: Larger pipelines or tanks often need a longer probe (i.e. jacketed tanks or pipes), in those scenarios, the client should also use an FPC sensor.

Figure 6: SRV Flange installation.

 3.3 When should you use a Long Insertion Sensor (X5) instead of a short flange sensor?

  • Installation with long standpipes.
  • Installation at a tank’s roof and short sensor can’t be fully submerged.
  • Jacketed walls in tanks or reactors.
  • Elbow and cross-pipe flange installations