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Polypropylene Manhole  DN 1000  for measurement of sewage water flow

mark of manhole  :   MS-Q / x / y/ p/ o / k / na / hs /


- Measurement type TCM 142/95-2075  , certificated by the Czech Metrology Institute

- Certification TaZUS 090-013151  , No. 90-130148 from 16.5.2005, static construction approved

- Calibration list for each measurement manhole

- Certification of water tightness DIN 4034

1.  Purpose and function of the measurement manhole 

Manhole with measurement equipment is designed for determination of water flow volume in the channels with an open surface ( e.g. in the channels, tubes, partly filled pipelines, creeks). The range of measurement starts from 0,1 l/s for the smallest  Parshall flume P1 up to 55 l/s for the greatest one P3.

            Polypropylene manhole can be loaded with maximum weight of 260 kg on the lid ( cannot be used for the streets with car traffic). The lid of the manhole meets the standards of  B125 - ČSN EN 124 class. There are two construction types, one for places with a high level  of underground water table and the second one is designed for places without underground water. The maximum depth of manhole is 2 meters. Manhole is watertight (according  to DIN 4034).

            The flow volume is measured by using Parshall flume . The size of the flume is chosen according to its operation range.


Size of Parshall flume

Flow (l/s)

Type of water



Parshall flume  P1



Mechanically  treated

Parshall flume P2



 Municipal sewage

Parshall flume P3



Water  coming into the flume  is forced  by  a bottleneck and by a subsequent bottom dip to pass over a critical  depth where it  goes from river-speed motion into rapids-speed  motion.  Thanks to this transition from one regime to another,  water flow  can be measured  from the water depth before the neck.  Water levels  are scanned either inside the gauge  shaft, which  is a part  of  the Parshall  flume,  or  inside  the  axis  of the  inflow part of the flume.  Inside the shaft, levels  are  gauged by a  float  linked by the mechanical transmission with a flow meter,  or by the sensor of  an electronic flowmeter.  In the flume axis, levels of water are scanned by an ultrasonic  sensor.  The electronic flowmeter converts  data  about  flume water  depths to flow rates and volumes. The standard Parshall flume is produced without  a gauge shaft.

            New electronic evaluations units provide: data storing, statistic data treat and other calculations. Data can be sent to internet servers or directly to the computers as well as to the mobile phones. Some of the units can control the waste water treatment plant technology or control the valves or  chlorine dosage pumps and etc.

2. Advantages

Manhole with flowmeter is convenient solution especially for places where simplicity of assembling is required. Manhole can be equipped and delivered with electronic sensor and electronic evaluation unit. Electronic equipment is fastened  inside of manhole and protected for transport. Calibration is done at the production hall and so no further checking of measuring device is required. This solution of measuring is the most effective.

1.1.    Manhole DN 1000

- higher speed and simplicity  of design and manhole assembling on the site
- higher construction safety 
- higher measurement precision
- precision of production in the factory hall is more effective than in the field
- polypropylene manhole is resistant against acids, lye or other chemical agents

1.2.   Parshall flume

The Parshall  flume  is a measuring device of the volume flow rate with a wide variety of  use.  It can be installed  in a stream,  drainage, irrigation  canal,  reservoir outlet, sewer system, waste-water treatment plant, etc.  Its  broad applicability  is mainly due to these advantages:

small energy  losses ( 3-4 times smaller than in a weirs),
high insensitivity to velocity distribution profile at the inflow,
ability to withstand high  degrees  of  submergence (up to 0,7),
velocity of flow through the flume  is sufficiently   rapid   to  prevent  suspended solids sedimentation,
minimal maintenance costs,
broad range of  flow  measurements
long lifetime
the deviations is in the range from 3,8 % to 2,2% for minimum and maximum of flow on the level of probability 95 %

3.  Technical parameters of manhole and Parshall flume

Exact hydraulic calculations for placement of Parshall flume can be done free of charge  Pars aqua

( tel.  + 420 736 686 159, pars@pars-aqua.cz).

Polypropylene Manhole DN 1000 is equipped with a flowmeter Parshall flume (sizes P1,P2 or P3).  Inlet and outlet pipes vary from DN 200 up to DN 400 and can be attached to different pipe materials. Rectangular lid of the manhole (600/600 mm) is made of plastic and meets  the class  B 125 - ČSN EN 124. The ceiling of the manhole is placed 210 mm below the cup. Manhole is equipped with stainless ladder.

 Construction is designed for two modes of applications :

 a/   type with underground water - table

 b/   type without underground water - table

ad a/  manhole with undegroud water - .type - MS - Q /water/

manhole is welded from 8 mm thick polypropylene plate. Cylinder   shape DN 1000 mm is made with deviation - 10 mm. Construction is watertight according  to the norm DIN 4034. The bottom of the manhole is placed 306 mm under the bottom of the inlet pipe.

Strength of manhole and its resistance against the water pressure is ensured by:

-         buffles placed around the cylinder
-         circumferential concrete cylinder (diameter 1240 mm, height 810 mm)
-         concrete filled manhole bottom (up to the upper desk of Parshall flume)

ad b/ manhole without undegroud water - ..type - MS - Q /drought/

the construction is similar to the one described above but without the circumferential concrete cylinder

Static calculations :

Static calculations were made by software Nexis 32 for these parameters:

- sand around the manhole r = 1800 kg/ m3 ,

- parameter of internal friction given by ČSN EN 12566-1 čl. 5.2.1 Ko = 0,33

- loading of the surface around the manhole  2,5 KN/m2

- loading of the lid with persons up to 260 kg

- depth 2100 mm

Picture describes mathematical results of tension and deformation.

3.1.  Dimensions and parameters of manhole

The multiparameter signing is used for description of the manhole parameters and its dimensions, These dimension are significant for production.

Manhole type

  MS-Q / x / y/ p / o / k / na /hs /                    

where :

    Sort of parameter and its description



Undeground water occurrence  

- /drought/ - /water/

y Type of  Parshall flume e.g - P1 - P2 - P3


Diameter and material of inlet

e.g. - DN 300 Bocker


Diameter and material of outlet

e.g - DN 400 PVC


The vertical distance  between  IN and OUT  pipes

e.g - 50 mm


Distance between Parshall bottom and the inlet pipe bottom

e.g - 25 mm


Depth of manhole from edge of lid to the inlet pipe bottom

max. - 1704 mm

See picture above

Example for your order:

MS - Q / drought /P1/ DN 300 Bocker / DN 400 PVC / 36 mm / 45 mm /1600mm

3.2.   Mechnical paramaters - metrology part

3.2.1.      Parshall flume - more informations here






Qmin (l/s)




Qmax (l/s)





max 0,6 











































Consumtion curve :    Q  =  a * h


m - weight of flume (kg)
hd/h - ratio of water submergance ( - )
h - water depth measured at the distance B´ in front of the throat (m) 
hd - water depth behind the flume (m)
W,B´  aľ   V - dimensions of flume (see pic.)  (cm)
Q - .flow water (m3/s)

Consumtion curve

Standard curves  Q = fce (h) are given in the table and in the enclosed graphs. Parshall flume is produced with certain deviation (Metrology rules for production TCM). Influence of this differences is eliminated with using calibration method. Each Parshall flume has its own calibration list which is at the and of this booklet.

Accurasy of measurement

            Flowmeter parshall flume was tested in Czech Metrology Institute and obtain certification TCM 142/95-2075  No. 2075/95/1 from 1. june 1995 (validity periodically prolonged). The deviations of measurement is in the range from 3,8 % to 2,2% for minimum and maximum of flow on the probability level 95 %.

(deviations are calculated for depth measured with deviation - 0,2 mm)

Design of  Parshall flume

            Right conditions at the inflow and at the outflow pipe determine its proper function. At the inflow should be river- speed motion conditions. Inserted Parshall flume raises water level and lowers speed motion . Velocity has to be high enough to prevent sedimentation of suspended solids. The placement of Parshall flume for creek-speed motion has to be hydraulically calculated (realize free of charge Pars aqua) .The streaming in front of flume should be smooth,  free of whirls and undulation, to provide a well balanced speed distribution profile.  For these reasons, the flume  should be  installed at a safe distance from the end of  a curve  (at least 12 W), or for the drop wall at least 30 W (depends on the depth and on the schape of floor)   . Exact calculation of these distances are given at our web pages www.pars-aqua.cz. (only in czech version ). Complicated designs can be done at Pars aqua .

At the outflow end of flume , sufficient outflow conditions must be secured to prevent excessive submergence  (maximum submergence ratio  is listed in Tab. 1 - parameter hd/ha).  Discharge equitation has to be adjusted if  those values are exceeded !

            Since correct functioning of the  Parshall flume  depends  on  correct hydraulic design of the track  and  on  proper mounting,  the job should be assigned to a specialist, or  otherwise PARS aqua should be consulted. We are making these calculations free of charge and have established system of questionare which  simply can solve design via email.

Maitanance and operations conditions

Parshall flume

The Parshall flume is designed to measure the flow of  water  and, consequently, although it is temperature-resistant, the water in the flume must  not be allowed to  freeze up.  The maximum water temperature is 80 degrees Celsius.  The flumes  resist inorganic salt and acid solutions, alkaline solutions without  too strong  oxidising  properties, and  a majority  of organic  solvents.  As far as operational  maintenance is concerned, the flume requires once-a-year cleanups of its surface and of  the float shaft and of  the connecting pipe between shaft and flume. The maximum size of derbies which are able freely pass the flume is calculated as 0,8 x W ( 80 % of the throat). For greater quantities of unsolved substances, screens should  be adjusted.


Measuring manhole serve for measuring of water flow (newton¶ parameters) for channels where water do not freeze and flow with open surface. Manhole has to be placed under ground for cases where manhole is partly above the ground certain deformations can occure. These deformations do not influence precision of measurement . Device maintenance and control has to be done periodically (lag time vary case for case), then manhole has to be well ventilated  to prevent occurrence of danger gases.

4.    Assembling of manhole

Assembling of manhole is simple and easy. Follow the mounting steps :

- Manhole is placed with using crane on concrete bed (declination from horizontal level at maximum 5 mm/1000mm, roughness at maximum 2 mm)

- Concrete bed foundation is 306 mm under the bottom of inflow pipe,  ( the design of concrete foundation depends on actual ground conditions and has to be designed by desiner of the whole project)

- Manhole¶ pipes are tightly and with sufficient strange fastened to the mains ( the system of connections is used according  material of mains pipe - .see table



Systém of conncection



Hobas fittings for connection  two pipes edges (e.g. DN 300/DN 300) - delivered with manhole



pipe      silicone    concrete     pipe


with rubber seal






Bocker fittings for connection  two pipes edges   (e.g. DN 300/DN 300) - delivered with manhole



 Commercially produced fittings for connection  two pipes edges is used (e.g. DN 300/DN 300) - delivered with manhole


The pipes connections has to be adjusted with concrete with thickness at minimum 15 cm in the lenth 50 cm at minimum.

- Concreting of manhole
- space around Parshall flume is fulfil up to the level of upper desk of Parshall flume with concrete B20 (stones diameters up to 1,5 cm) . Surface of created bench is sloped to the channel  (in case of floods water can return to the dich bed )
- circumferential concrete cylinder (external diameter 1240 mm, thickens of concrete layer 100 mm, height 810 mm) - only for manhole with underground waters
- or passages with tiles the ceiling is reinforced with layer of concrete B30 and with iron   (iron network 8 mm, 100/100 mm distance)
- round is placed carefully andy symetrically  (recommended layers  50cm) around the manhole so that the forces do not shift it
- the instalation of the bracket with ultrasonic sensor is mounted to position B´ in front of the flume throat (cross buffle at the Parshall inlet is cut off),  wires leading to sensor pass the manhole wall with fitting (water resistance IP 66 )

5. Evaluation of flow

The following  types  of flowmeters  are  usually  used  to convert  water-depth  data in  the gauge profile:

a)  mechanical device without a data  recorder,

b)  electronic device with an ultrasonic  surface scanner

Mechanical  flowmeter

            Parshall flume can be equipped with brass ruler with cutings to the metal plate. This equipment serve only for actual flow readings and simple checking of the electronic flowmeter function. Brass ruler hs to be ordered separately

Electronic flowmeter

            The electronic  flowmeter is a device which consists  of a scanning probe and a microprocessor-based  evaluation unit.  The  scanning  probe with an ultrasonic transmitter/receiver is placed  in  the flume  axis in the profile B´ . The sensor is positioned above maximum  water  surface (vary  from 20 cm to 60 cm ).  The probe has to be cleaned within six months  from  incrustations and other impurities. The evaluation unit  is usually separated and placed at the building. Some equipment has evaluation unit as a part of sensor and so the data is displayed in the manhole. Each producer has its own regulations and conditions for instalation . Nowadays flowmeters are offered  in many variants (data storing, statistic data treat and other calculations, wireless data transfer to internet servers or directly to the computers as well as to the mobile phones,  control of the waste water treatment plant technology or control the valves or  chlorine dosage pumps and etc.

            The flowmeter is not  part of the Parshall  flume and  has to be ordered separately.

Warranty conditions

If  conditions stated  above  are observed,  the company  provides Parshall flumes with a warranty  period  of  two years  from delivery date.

Calibration List

                                 Parshall flume        No.  - - - - ..

according Czech metrology law 505/91 Sb.

Costumer  :

Place of usage  :

Measure tool :    Parshall flume     P - -        No. - - -

Function and parameters : Parshall  flume is measure tool used for determination of water flow volume in the channels with an open surface ( e.g. in the channels, tubes, partly filled pipelines, creeks or other streams). Water  coming into the flume  is forced  by  a bottleneck and by a subsequent bottom dip to pass over a critical  depth where it  goes from river-speed motion into rapids-speed  motion.  Due to this transition from one regime to another,  water flow  can be measured  from the water depth before the neck. Water depth is measured in  a certain distance B´ in front of the throat . Volume of flow is calculated using the exact mathematical formulae Q = a * hb . Parameters a, b is the matter of this calibration list.

Sort of measure tool : working measurement device  ( no-legal)

Calibration method: comparison geometrical parameters  with Certification TCM 142/95-2075  , approved by the Czech Metrology Institute

Used mesuring devices and its calibrations :

- steel roller,  lenth  60 cm , readings  0,5 mm, deviation 0,1 mm   Tajima

          Certification List  ČMI  č. 6033-KL-D156-04 from 4. may 2004

- roller No. č. 90124, lenth  60 cm , readings  0,1 mm, deviation 0,02 mm 

Certification List ČMI Brno č. 6033-KL-D158-04 from 4. may 2004          

Calibration Results  :

 Dimensions and other geometrical parameters meets the standard given by Certification TCM 142/95-2075  , approved by the Czech Metrology Institute

                        Average throat wideness        W =                cm

 Consumtion curve :

                                                             Q =                  * h            [m3/s, m ],

            h - (m), depth measured at the distance               cm in front of the throat

            Q - (m3/s)   volume of flow,                            

Deviation of measurement :

The deviations of measurement is in the range from 3,8 % to 2,2% for minimum and maximum of flow on the probability level 95 %, calculations of deviations are made according EAL-R2 a ČSN ISO 3354, ČSN ISO 9826, ČSN ISO 1438-1 a ČSN ISO 5168.

Calibration executed by : Ing. Jan Vrąecký, Csc ,     tel. + 420 736 686 159

                                        Pars aqua Ltd,   Strojírenská 260,   155 21 Praha 5


(c) 2015, PARS Aqua, s.r.o.