1. What way of cutting packing do you recommend?

For pumps we recommend an angled butt cut with approx. 75 degrees, which results from the different circumferences of Stuffing box ID and OD with an circumferential over length adder of approx. 9% for small shaft dimensions and 4% for big shaft dimensions.

For valves and reciprocating pumps we recommend a 45° skive cut with a circumferential adder of approx. 2%.

2. Why are some valve packing rings produced with butt cut?

The reason is, that some valve packing styles have no or little cross section impregnation and tend to fray. The 75° butt cut is the shortest way through the packing and minimizes the risk of fraying.

3. What is the advantage of precompressed rings?

First we need to clarify the wording: Precompressed.

It means that a individual ring is densified in a die to its working density. Other expressions like preformed, die formed, precut or similar do not necessarily mean a densification has taken place.

The advantage is that all installed rings will have the same density and will react more promptly on gland pressure. As a result, less gland pressure is needed. The cut will close up better and additional over length to compensate shrinkage and to seal the OD better is easy accommodated in a die. In operation the settling of the ring stack is less and a longer way of adjustment is available at the bolts. 

4. How important is it to observe temperature limits displayed in the technical parameters of a packing?

The limits should consider the weakest component in a packing. A carbon fiber may have a temperature capability of 400°C/750°F but the cross sectional impregnation maybe for example PTFE, therefore the limit is reduced to 280°C / 550°F. Not observing the limit will result in decomposition of PTFE and the resulting split products can attack the stuffing box components and harm the health of people working in the area.

5. What is the advantage of life loading?

Life loading is used on valve gland bolts at pressures above 16 bar/200 psi. The Belleville Springs have a linear spring load and compensate compression loss on the packing stack due to wear settling or thermal expansion. If life loading is not used a failure in not adjusting the gland bolt's can result in mechanical destruction and blow out of the packing when compressed products expand rapidly.

6. How can I section the right packing for my application?

First select if it requires a pump, valve or special packing. Consideration must be done on the temperature of the application. The technical figures give guidance. An important criterion is the available shaft hardness expressed for most products in HRC. Further information is available on pressures, pH range and shaft speeds. Important is if the product contains solids the characteristics will describe that. If dry running can appear, packing with high heat conductivity and which runs on a softer surface is preferred.

7. How does the max shaft surface speed figure expresses in m/s or fpm influence the packing performance?

This figure needs to be understood in combination with pressure to be sealed. If the pressure is low, even packing with a low heat conductivity, due to missing carbon content like aramid fiber packing, can run higher shaft speeds. In principle the higher the carbon content of a packing the better its capability to high shaft speeds. Pure PTFE packing runs lowest speeds, carbon and graphite packing run highest shaft speeds.

8. How important is the max pressure parameter given in the technical data section?

The given parameters are based on the ability and strength of the packing not to extrude. The value is determined on the recommended gap width between gland ID and shaft and SB bore. These are 5% of the used packing cross section for pumps and 2% for valves. Nigger gaps will reduce the pressure rating and vice versa. Higher temperatures can as well reduce the values with many packing styles mainly PTFE packings or PTFE impregnated packings. 

9. Is there a difference between 5mm and a 3/16" packing?

Typically 3/16" is a 5mm size and vice versa. The braid of these sizes is 2-track and therefore very pliable. Imperial braiders sell 3/16" as 5mm in Europe and metric braiders sell 5mm as 3/16" in US markets. As well only a small difference is found with 16mm and 5/8”, 19mm and 3/4", 22mm and 7/8", 25mm and 1".

An individual size should be braided for 6mm and 1/4", 10mm and 3/8" and 12mm and 1/2".

10. How important is the shaft or shaft sleeve material and the surface finish when choosing a packing?

In principle exist for all pump packing qualities we supply, recommended measurements for the shaft hardness in HRC hardness Rockwell. If slurries are the product to seal, automatically a harder surface should be chosen, as well considering the chemical aggressiveness. Some of the surface treatments will attack surface coatings. In principle the result of running a soft packing on a soft sleeve against abrasives maybe better, than ruining a hard packing requesting HRC 50 and more in the same application against a soft sleeve which only offers HRC 25.

11. Remove old packing or just add new rings?

In principle this is a marketing idea aiming for an understanding that eventually less maintenance is required. All good working practice would say, remove and inspect SB and sleeve condition.

12. Why are rings often in a different height than ordered?

For die moulded rings it makes a big difference if the same crossection packing is formed around a 30mm or 100mm ID and makes 30 x 50mm or 100 x 120mm. The smaller ring will bulge out and creates a bigger height and the bigger ring will tend to be smaller height.

Packing with a high percentage of run in lubricant will tend to bounce up in height after compression and a dry packing will actually be densified. Multiple bending rings may open as well the height.

13. What is the idea behind combination braided packing made of 2 different materials?

In principal we differentiate between corner- and running track reinforced hybrid packing. Two different yarns are used, one may have reinforcing characteristic like aramid yarns, and the other may have high graphite content for improved heat transfer capability. Corner reinforcement makes sense in applications with axial movement for example in plunger pumps. An additional side effect of corner reinforcement is to prevent against extrusion of packing in bigger gaps.

14. What advantage do running track reinforced packing offer?

In applications with rotating shafts running track reinforcement is preferred over corner reinforced braided packing. The reason for that is the reinforcement material is over the complete packing surface equal distributed, which leads to a reduced wear on shafts. A side effect is that solids in a sealed product are stopped in their dynamic activated by shaft rotation and this prevents the wear of the softer example heat conductive component of a hybrid packing.

15. What sense do bull rings make in pumps?

In pumps so called bull rings of wear resistant packing material are placed as bottom ring in a stuffing box when sealing products with solids to secure softer packing. If a lantern ring is used to flush the packing chamber for example water often the wear resistant packing is used from stuffing box bottom up to the lantern ring. The softer packing is then used from lantern ring up to the gland and will run in clean fluid.

16. Why use bullrings in valves?

The packing is axially put under compression, to activate a radial acting sealing force. If the gaps between gland or stuffing box throat and valve stem is bigger than 2% of the used packing dimension, the risk exists, that packing material will be extruded through the applied compression in the gap and the sealing force is reduced. Especially thermoplastic material has a tendency to extrude. As well expanded graphite foil packing is exposed to the risk to shear off its first layer into the gap as the foil thickness is only between 0,4 and 0,5mm. Bullrings made from extrusion resistant material will prevent gap extrusion and support the sealing performance of the packing. Due to tolerances in valve parts especially after revision it can be found that the recommended 2% maximal gap width is not kept in general and bullrings are recommended to use.

17. What value to gain from reduction of stuffing box depth in valves?

Previous valves had often stuffing boxes housing 7 and more packing rings. Today’s experience with modern packing material limits the recommended amount of rings between 4 and 6 depending on the sealed pressure.  The rest of the available space in a stuffing box is filled with distance rings made for example from 2 pressure resistant filled carbon. These rings are usually split in 2 halves for ease of installation. As well other temperature and pressure stabile materials can be used. Physical sense behind this measure is to distribute the available compression force from the gland bolts more equally. A reduction from 7 to 5 rings can result for an internally rough packing with a low K-Value = distribution factor of applied axial force into radial sealing force of a packing in less than half gland pressure. This reduces the risk of extrusion of packing material between gland and stem and still delivers the same compression at the bottom  product next packing ring.

18. How is the effect on yarns with integrated reinforcement?

First it needs to be differentiated if the reinforcement is a processing aid or out of technical view an improvement of the application characteristics.

A processing aid can be viscose fiber content supporting the spun process of recycled aramid fiber yarns or on expanded graphite yarns of the first generation a glass or cotton carrier. These contents should be low as they result in chemical and/or thermal caused volume losses.

A technical reinforcement improves the packing in an application. Expanded graphite yarns of newer generation have an integrated carbon fiber or integrated or over knitting reinforcing ultrathin inconel threads, which raises the pressure capability and eases quite substantially the extraction of used packing material from the stuffing box.

PTFE yarns with an integrated reinforcement rise in the packing the compactness, wear resistance and safety against extrusion.

19. Is it possible to use a pump packing in a valve application?

In principle this is possible and depends from the application values. Pump packing usually has a 15-25% content of run in lubricant, which will leave the packing in relation to temperature and compression.

Multiple readjusting of the gland follower is inevitable. Once all oil has left the pump packing it will operate stabile. An important side effect of run in lubricant is in a positive way that pump packing is easy to install and compresses easily, wherein in a negative way it will extrude more easily though gaps between gland and stem. Therefor bull rings are necessary to prevent extrusion.

20. Is it possible to use valve packing in dynamic application?

This is as well possible. Valve Packing implements no run in lubricant, which will leave the typical oil impregnated pump packing under high compression, herewith reduces the load on the packing and secures it against burning.

Through the absence of run in lubricant a valve packing should have in a dynamic application a very high heat conductivity like expanded graphite packing.

21. Why do the actual values meter/kilogram or ft/lbs vary often to the catalog values?

Most packings consist of yarn and impregnation like PTFE and oil, which are applied in different dipping processes. The content may vary depending on tension in the yarn and as well during braiding of the packing. A typical band width can be +/-15%. The braider endeavor with control mechanism on the braiding machine to compensate this but a remaining deviation is inevitable.