Frequently asked questions about piping systems
BASIC CONCEPTS FOR PRESSURE NETWORKS
The denomination PN in plastic pipes is inaccurate, since these, with the increase in temperature, do not keep the hydrostatic stress curve constant.
In any case, if we pay attention to the definition proposed by the CTE for Nominal Pressure, for example PN 20: "20ºC temperature, 20 kg pressure (20 bars) and life time 50 years", we can evaluate the behaviour of the pipe, seeing the admissible pressure of the same for the service conditions of 20ºC during 50 years.
The UNE-EN ISO 15874:2004 Standard "Piping systems in plastic materials for hot and cold water installations: Polypropylene", does not speak of Nominal Pressure (PN), but establishes the term "series".
The term "series" is defined in the standard UNE EN ISO 15874:2004 "Piping systems in plastic materials for hot and cold water installations: Polypropylene", and is a dimensionless number that fulfils the following equation (rounded to the first decimal place).
Serie (S) = (dn – e)/(2*e)
dn is the nominal, outside diameter of the pipe. e is the nominal pipe wall thickness.
The term "SDR" (Standard Dimension Ratio) is defined as the ratio of the nominal diameter to the thickness of the pipe.
SDR = dn/e
dn is the nominal, outside diameter of the pipe. e is the nominal pipe wall thickness.
Pressure losses are those pressure losses caused by the friction of the fluid against the pipe walls during the transfer of the pipe.
Class" means the optimum, but not exclusive, application for which the pipe has been designed, under a service life of 50 years. The same type of pipe may be classified for different application classes.
This classification is taken from the ISO 10508 Standard and the fields of application given shall be understood as indicative.
The classification is as follows.
- Clase 1: pipes for the supply of domestic hot water at 60 °C.
- Clase 2: pipes for the supply of domestic hot water at 70 °C.
- Clase 4: underfloor heating and low temperature radiators.
- Clase 5: pipes for high temperature radiator heating.
It is also called butt welding. Recommended for large diameters, the joining system is by heat and is carried out at the tube-tube or tube-fitting joint from the front.
Pipe and male fittings.
This coupling and fitting system is recommended for large diameters. It consists of passing current through the loops of the electrofusion fittings (male pipe, male fitting and female electrofusion fitting).
Molecular fusion joining system for pipes and fittings. It is performed with a polyfusion and heating dies. Male pipe and female fitting.
This joining system is used for diameters from 20 mm to 160 mm.
Operating pressures vary depending on the raw material used. For the same wall thickness, PP R is lower than PP RCT and PP RCT RP is lower than PP RCT RP.
It must be taken into account that the series (pipe thickness to compare these pressures) also has an influence.
Permissible pressures for:
ABN//INSTAL CT FASER RD
ABN//INSTAL CT FASER RD FIRE
Allowable pressures for:
ABN//INSTAL CT FLEX RD
| Pressures in bar at 50 years of operation | ||||
| SERIE | 20 ºC | 60 ºC | 70 ºC | ** 80 ºC |
| 3,2 | 31,7 | 17,7 | 14,9 | 12,7 |
| 5 | 20,3 | 11,3 | 9,5 | 8,1 |
| 8 | 12,6 | 7,1 | 5,93 | 5,1 |
| Pressures in bar at 50 years of operation | ||||
| SERIE | 20 ºC | 60 ºC | 70 ºC | ** 80 ºC |
| 3,2 | 20,3 | 11,3 | 9,5 | 8,1 |
| – Polypropylene-homopolymer PP-H (also known as type 1) | PP-H comprises all homopolymers of polypropylene; |
| – Polypropylene block copolymer PP-B (also known as type 2) | PP-B comprises thermoplastic propylene block copolymers, containing not more than 50 % of other olefinic monomer(s), or of any functional group other than the olefinic group, copolymerised with propylene; |
| – Random polypropylene-copolymer PP-R (also known as type 3) | PP-R comprises random thermoplastic propylene copolymers containing not more than 50% of other olefinic monomer(s), or of any functional group other than the olefinic group, copolymerised with propylene; |
| – Random polypropylene-copolymer with modified crystallinity PP-RCT (also known as type 4) | PP-RCT comprises random thermoplastic propylene copolymers containing not more than 50% of other olefinic monomer(s), or any functional group other than the olefinic group, copolymerised with propylene. olefinic monomer(s), nor of any functional group other than the olefinic group, copolymerised with propylene. |
DRAINAGE
Areas of application
SN 2 pipes and fittings must not be installed in areas where hot water discharges occur. The non-pressurised sanitation standards define two series or areas of application:
U - Application area code outside the building structure, up to 1 m from the building, in which the sanitation pipe system is connected.
D - Code for buried application area, both inside the building structure and outside the building, from 1 m from the building where the pipes and fittings are connected to the building's discharge system.
These standards also indicate the classification of pipes and fittings that can be used in each area of application.
Note: The pipe classes SN 4 and SN 8 are suitable for both applications and can therefore be marked UD.
The Nominal Stiffness (SN) is the resistance to crushing of a pipe or fitting under the conditions defined in the UNE-EN-ISO 9969 standard.
In a sewerage network without internal pressure, the pipes are subjected to external loads, due to the backfill material of the trench and the moving loads of traffic and upward forces if there is groundwater. These loads cause the pipe to tend to deform, resulting in compressive stresses on the inside of the pipe and tensile stresses on the outside of the pipe, which have to be supported by the pipe structure.
| | POSITIVE PRESSURE | PRESIÓN NEGATIVA NEGATIVE PRESSURE (DEPRESSION) |
| ABN//EVAC ENERGY PLUS | + 1 bar | -0,9 bar |
| ABN//EVAC HT PHONO | + 1 bar | On trial |
DECIBLES
When we speak of decibels as a synonym for quantity of sound, this is a mistake. The decibel is not a unit of sound measurement.
The decibel (dB) is a relative unit, used to express the ratio of the quantity of interest to a reference value. It does not in itself represent a value on an absolute scale: the reference must be indicated.
In the same way that we do not hear decibels, but sound pressure oscillations (vibrations of air particles).
The decibel is NOT a unit of sound measurement.
P: effective pressure (Pa) P0: reference pressure = 20-10-6 Pa
Because the range of sound pressure that the human ear is capable of picking up is so wide that it has been compressed into a scale with a range of 107 units (10-6 , 10-5 , 10-4 ,...., 10) , ranging from the so-called threshold of hearing (20µPa) to the threshold of pain where the eardrum ruptures (200Pa), to only 140, which is much more manageable. But BEWARE!!!, we are talking about a scale that is not linear, but logarithmic. And this is when we start talking about dBA.
And how it best represents how changes in sound intensity really feel to the human ear.
Imagine a building 80 metres high. If we were to extend its height by a further 10 metres (90m in total), it would appear to the eye to be only slightly taller because we have actually increased its height by 12.5%.
If we translate these magnitudes into dBA, if a sound is 80 dBA louder, adding an additional 10 dBA would make the sound 10 times louder; about twice as loud to our ears.
It will depend on where we are in front of the sound source.
The dBA is a unit of sound pressure, a measure of force and more specifically a measure of force per unit area.
Every time we move away from the sound source, the sound loses intensity at a rate of 6 dB each time the distance doubles.
Example: If at one metre we perceive 80 dB, at two metres we will perceive 74 dB, at four metres 68 dB
and at eight metres, 62 dB).
It is therefore important and fundamental that when measuring sound pressure intensity, the distance at which it is measured is indicated, and this is where the dBA comes into play.
