What products are involved?
SRV - Inline Viscosity Meter
What is the purpose of this article?
To give guidance on the installation of a G1/2” SRV sensor (SRV-X1-12G).

1. Introduction

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

The industrial G connection is a cylindrical thread connection that follows the norm ISO 228. It is also referred to as BSPP (British Standard Pipe Parallel). It requires an O-ring for correct sealing. A Ø17.86x2.62mm O-ring is used for standard installation of the sensor.

The SRV with the G1/2” thread connection has the order code SRV-X1-12G. This sensor variant has different accessories available such as a flow-through cell and weldolets (useful for flush hygienic installations). These accessories are detailed below.

Figure 1: SRV G1/2” dimensions


Rheonics SRV 

Order code
Connection type
G 1/2"
Drawing and CAD file

SRV-G1/2” CAD file 

2. General installation guidelines

SR-sensors can be placed at any point in a process and at any orientation but the following considerations should be observed to ensure stable, accurate, low-noise measurements.

2.1 Submersion

The 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 is a potential problem when flow rate is low and the pipe isn’t full.

A possible solution is placing the sensor horizontally and parallel to the fluid (e.g. in an elbow) and not vertically and perpendicular. When the possibility of insufficient submersion exists, then placing the outlet of the flow cell higher ensures that the flow cell is full for the sensor to make proper measurement. However it should be noted that you may need proper drainage of the flow cell and avoid sedimentation in the flow channel around the sensing element. Also, the use of the HPT-12G flow cell accessory can be considered for the SRV-12G, explained later in this article.

Figure 2: SRV-X1-12G sensing area

2.2 Stagnation/dead zone

It is not good practice to have dead or stagnant zones around the sensing area (Figure 2). These are defined as any space, inside the red zone, where fluid transport is insufficient leading to immobile fluid, as well as possible accumulation of solids and deposits, or unwanted material like air. These all have negative effects on the measurement.

A clearance of at least 5mm is recommended between the SRV 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. For processes with non-constant flow rates, the recommendation 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). Installing the sensor upwards can solve the issue of non-full pipes but should not be considered for fluids with solids or characteristics that can create deposits around the sensing element. Using the flow-trhough cell HPT-12G is also of great use for low flow rates.

In all cases, the SRV’s sensing element should be submerged in the fluid in motion. It’s best to avoid installations with long standpipes (i.e. using a long weldolet or tee), since that may lead to not good fluid transfer resulting in measurements that do not reflect the true state of fluid or worse high noise measurements.

Figure 4: SRV-X1-12G installation indications

3. Installation options

3.1. G1/2" Weldolets - HAW accessories

The HAW line of Rheonics weldolets enable the installation of the SRV-12G in tanks and pipes (also suitable for the SRD). These weldolets have two versions, for thin walls (around 1.5mm) and thick walls (max. 10mm), and each one has two further variants for Ø16.1x1.6 mm O-ring seal and metal-metal seal. 

These accessories are suitable for flush hygienic installations.

  • HAW-12G-OTN: Weldolet with a Ø16.1x1.6 mm O-ring seal for thin walls
  • HAW-12G-MTN: Weldolet with metal-metal seal for thin walls
  • HAW-12G-OTK: Weldolet with a Ø16.1x1.6 mm O-ring seal for thick walls
  • HAW-12G-MTK: Weldolet with metal-metal seal for thick walls

Figure 5: HAW-12G-OTN

Figure 6: HAW-12G-OTK


3.2. Threaded port on pipe or tank wall

Another installation on wall, is by creating a threaded hole in the pipe or tank for the sensor. Installation requires a Ø17.86x2.62 mm O-ring.

In tank installations, it is recommended to place the sensor at a level that has always fluid. The entire sensing element must be submerged in the fluid so it can also be placed at a tank’s bottom. Potential issues could be that the fluid oscillates between static and moving conditions which can change the apparent viscosity of the fluid itself. Also, some fluids can create deposits on the wall. The sensor is affected by these layers created by the fluid’s reaction. This is usually solved with an FPC (long insertion sensor).

Figure 7: SRV G1/2” with O-ring mounted in a wall


Steps for installation in walls:

A hole with G1/2” threads is needed in the wall. 

i. Place the Ø17.86x2.62 mm O-ring seal on the sensor, so it fits the notch of the sensor just above the thread.

Figure 8: SRV G 1/2 with O-ring

ii. Insert the sensor into the female thread part. Manually, give it enough turns until noticing the correct sealing with the wall or adaptor pressing against the O-ring.

Figure 9: SRV G1/2” in wall drawing

3.3 Flow-through cell HPT-12G

Rheonics accessory HPT-12G is recommended for an inline installation of the SRV G1/2” in high pressure aplications, especially in small line pipes. Visit its accessory page here.

This accessory requires the use of a different O-ring, also supplied by Rheonics, with a dimension of Ø15.1 x 1.6 mm. This flow cell withstands high-pressure conditions (up to 500 bar) and ensures no dead zones around the sensor. Due to its G1/2” inlet and outlet ports, it can be used for small lines (e.g. DN20).

Steps for flow-cell installation:

i. Pleace the Ø15.1 x 1.6 mm O-ring in the notch of the flow cell, right after the conical section.

ii. Place the sensor in the flow cell and thread it in completely.

iii. Connect the flow cell to the line, possible connectors adaptors are HF/60-SWOS-12-DN12.

Figure 10: SRV in HPT-12G flow cell.