IN AIR · 33 kV and above · Insulcap RV
A sealed HV cable end in a hot yard builds gas
IN AIR, on a drum in a compound or stacked in a ship's hold: the one band on this site where what matters is coming out of the cable rather than going into it.
If you searched for oil and gas end cap seals, stop here
That phrase almost always means oilfield work — tubular, casing, wellhead and flowline sealing — and nothing here serves it. What is described below is a cable accessory: a shrink-fit cap that closes the cut end of a power cable on a drum. Take a wellhead or tubular enquiry to a pressure-equipment supplier. A cable-accessory catalogue cannot rate a part for that duty.
De-gassing end cap with relief valve, Insulcap RV
A heat-shrinkable end cap supplied with a relief valve, for sealing HV and EHV cable ends of 33 kV and above while the gas that evolves inside the cable during transport and hot-climate storage is let out. The body is the cross-linked polyolefin cap with a hot melt adhesive lining. The valve is what makes it a different part.
| Exposure band | IN AIR — drum store, open compound, ship's hold |
|---|---|
| Cable class | HV and EHV, 33 kV and above |
| Size codes | GEC 102 RV to GEC 801 RV |
| Cable range | 12–200 mm (roughly 0.5–7.9 in) |
| Valve opens | Above 3 psi, then reseats |
| Valve direction | Non-returnable — out only |
| Sealing | Hot melt adhesive lining, IP68 where specified |
| Continuous temperature | −40 °C to +110 °C (−40 to 230 °F) |
| Valve testing | Every valve tested for gas release before despatch |
| Sheaths served | XLPE, PVC, PILC and rubber-sheathed cable |
Heat is doing the work here, not water
IN AIR is the shallowest of the four bands and usually the least demanding. On this part it is the awkward one. A drum standing in an open compound through a hot summer, or stacked below deck on a long sailing, is not under attack from outside. The cable is making something inside itself, and the cap that keeps water out is the same cap that keeps that something in.
Gas evolves continuously inside HV and EHV cable while it is carried and while it is stored in a hot climate. Methane is the fraction that decides how the part is specified. Cap both ends of a 33 kV drum tight and the gas accumulates behind the cap for as long as the drum stands there — on an export order, months rather than weeks.
Two consequences follow, at different moments. The commercial one: the drum goes into a heating chamber to be de-gassed before anybody joints it, and how long it sits there depends on how much gas is still dissolved in the insulation. The other arrives at the knife. Methane held behind an end cap with no relief valve is described on the manufacturer's datasheet as a fire risk at the moment that cap comes off — and that is when a blade, very often a flame, is already at the end.
The valve answers both. It is not a drilled vent and not a filter. It lifts above 3 psi, roughly 0.2 bar, then reseats, so the end spends its storage life sealed except for the seconds it is bleeding.
What the valve does, and four things it does not
The limits matter more than the claims here, because the valve is an extra component on an otherwise simple cap.
- It lifts above 3 psi and reseats. Below that the cap behaves as an ordinary sealed end cap, nothing open to atmosphere.
- It is non-returnable, so moisture, water and dirt cannot travel back down through it. That is how the valve is built, not which way up the drum is stored.
- Every valve is tested for gas release before despatch. A one-way device on a sealed end is only worth having if each one has been proved to open.
- It does not de-gas the cable; it relieves pressure. What is claimed is less time in the heating chamber, not none.
- It is not the valved cap used on pressurised telecom cable. That variant holds a pressure in. This one lets one out.
- It is not published below 33 kV. On distribution cable the plain sealed cap covers the job and a valve only adds somewhere to fail.
- It is not a termination and not a cover for an energised end. It comes off before the joint is made.
Body properties, where heat is the load
| Property | Value | Test method |
|---|---|---|
| Continuous temperature limit | −40 °C to +110 °C | IEC 216 |
| Shrink temperature | 125 °C | IEC 216 |
| Accelerated ageing | 120 °C for 500 hrs | ASTM D2671 |
| Heat shock, 250 °C for 30 min | No cracking or flowing | ESI 09-11 |
The valved cap uses the same cross-linked polyolefin body as the plain one, so the physical and electrical figures — tensile, density, hardness, dielectric strength — are published once, on Insulcap cable end caps. The four rows below are the ones a hot compound actually loads. For what a test of this kind is evidence of, read what an end-cap datasheet proves.
Asked by despatch and by the jointer
Does the valve let us skip the de-gassing chamber?
What pressure does it open at, and does it stay open?
Do we need it on 11 kV or 22 kV drums?
Which size code do we order against?
Is it risky to cut a plain cap off a drum that has stood in the sun?
Next, in the order the decision is usually made
- End cap size chartA measured diameter into a GEC code.
- Insulcap cable end capsThe plain sealed cap — valve or no valve is the real choice.
- Cable end capsThe hub, ordered by exposure.
- Fitting a heat-shrink capTorch technique, and keeping flame off a valve crown.
- Cable drum despatch sealingWhere this decision is taken, at the works.
- Why end seals failTrapped pressure is one of the six.
Send the diameter and the voltage class, not the part number
A useful first reply needs four things: measured cable outside diameter in mm, voltage class, sheath material, and how long the drum will stand before jointing. The ordering variant list for the valved caps sits on the manufacturer's page for this part. Open End makes nothing; these caps come from Gala Thermo Shrink Pvt. Ltd., Mumbai.