A new generation of underground hydrants

With the new generation of underground hydrants, ERHARD GmbH & Co. KG in collaboration with the BAYARD company from France is bringing a revised design in two versions onto the market. PREMIUM with a PUR cone and fully enamelled casing pipe and STANDARD with an EPDM cone and EKB epoxy coated casing pipe are the names of the two versions, which offer maximum performance for the maximum security.

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PREMIUM DN 80 underground hydrant with PUR cone, enamelled

The hydrants of the new generation have numerous well thought out construction features which guarantee the user even more reliable operation and maximum security. Hence the shut-off cone is joined to the valve insert pipe by a secure bolt connection and so provides a reliable in the enamelled seating of the lower part of the column. Polyurethane (PUR) is a high-molecular organic material with a chemical structure characterised by a high number of urethane groups. Within determined temperature limits it therefore has the characteristic elastic properties of rubber and is therefore used in products under very high mechanical stresses. For its use in hydrants it stands out above all because of the very high tensile strength and elongation at break on the one hand and the low water uptake on the other hand.

Further advantages of the PUR cone:

• The material has an extremely high abrasion resistance and hence minimal wear (as shown in numerous long-term tests).
• Not sensitive to soiling in the cone seat; full tightness (especially in case of surface distortion due to foreign bodies) is guaranteed at all times and the working life is considerably increased thanks to the excellent resilience. 
• Very good tear strength, considerably higher than with comparable elastomers; extension of material damage therefore only to a very low extent. 
• Very high ageing resistance; this also means that leaks due to crack formation or brittleness are avoided over very long periods of use.
• Good sliding characteristics on account of the low friction coefficient; therefore only low torque values required for opening and closing. 
• Meets all requirements according to DVGW W 270 and KTW guideline and is free of plasticisers and fillers.

Corrosion protection of the casing pipe: permanently protected with ENAMEL

The PREMIUM design underground hydrant is offered with a fully enamelled casing pipe for perfect corrosion protection. The particular properties of enamel have been known for around 3,500 years when the first pieces of jewellery were made with it. And still today, enamel is indispensable as a technical material for industrial applications. When fired at around 720°C it presents itself as a glasslike, high-strength material which forms a permanent and inextricable bond with the metallic substrate. ERHARD enamelled valves have a special fibre enamel with short fibres in the material which prevent the enamel from cracking in case of damage.

Enamelling in accordance with DIN 51178 offers numerous advantages:

• Safely protected from possible infiltration
• Absolutely impervious to vapour and oxygen
• Stable bonding even under bending of the material and other loads
• High elasticity
• Resistant to acids, alkalis and neutral organic media
• Extremely temperature resistant, can be used without problem even with sudden temperature fluctuations
• Good resistance even with abrasive media due to high hardness of 600 HV
• Even with soil class III, no further protection measures necessary
• Extremely smooth surface (Ra 0.05) for hygienically impeccable conditions
• No fixing of mineral and/or organic elements (no growth of incrustations to reduce the cross-section)
• Ideal mating surface for elastomer seals
• Extremely durable and long-lasting, no embrittlement and chalking
• High environmental compatibility

The company has extensive experience and many years of knowhow in the complex process technology of enamelling. A modern enamelling plant allows flexible but high-quality production as all the stages of enamelling with ERHARD Pro-Email are seamlessly monitored.

The ERHARD DN 80 PREMIUM underground hydrant is available in the design with flange connection with the reliable claw cover in plastic, with and without double closure.

STANDARD DN 80 underground hydrant, EPDM cone, EKB epoxy

As compared with the PREMIUM underground hydrant, the STANDARD underground hydrant designed with an EPDM cone according to KTW guideline and DVGW W 270 – instead of PUR – and the casing pipe coated with epoxy-plastic (EKB) – instead of enamel.

Corrosion protection of the casing pipe: permanently protected with EKB coating

The STANDARD design is seamlessly protected by cataphoretic dip-coating inside and out. Cataphoresis is an electrochemical process in which the workpiece is coated n a dipping bath. The coating thickness is around 50 µm. The process is also used to ensure corrosion protection in vehicle production, i.e., it is extremely suitable for complicated contours. 

The most important properties are:

• In accordance with EN ISO 2808: impact strength 5 Nm (EN ISO 6272-1), 1 kg falling weight, height 50 cm, no cracks
• Salt spray test: 500 hours corrosion resistance (EN ISO 9227), no bubble formation
• Adhesion with the cross-cutting test: 0, no separation of the coating
• Threads are included in the dipping process and so also protected against corrosion

Particularly with the subsequent EKB coating, the result for this combination is an absolutely sure protection against corrosion. The total thickness of the powder coating applied is at least 250 µm.

Naturally, the new generation corresponds to EN 14339 for underground hydrants; both alternatives have the DIN-DVGW type approval certificate for drinking water and the CE label.

Author: Matthias Müller, ERHARD GmbH & Co. KG

The article was slightly shortened by the editors. You can find the complete article with various illustrations as a PDF in the download area under Downloads Annual Issues EADIPS FGR.