MAPLE SIRUP PRODUCERS MANUAL 



PLASTIC TUBING 



23 



With the advent of plastic tubing, most of the 

 objections associated with metal pipes have 

 been overcome. Not only can plastic tubing be 

 used for collecting and transporting the sap, 

 but also it is cheaper to install, it has greater 

 flexibility and elasticity, and it is easy to keep 

 clean. Wide acceptance of plastic tubing by 

 maple producers (.38) has been a major factor in 

 modernizing the 300-year-old maple industry. 



Use of plastic tubing has practically elimi- 

 nated the hard, unattractive labor of collecting 

 sap and has lowered the cost of sirupmaking as 

 much as 40 percent. No longer is it necessaiy to 

 construct expensive roadways through the 

 woods to support heavy tanks of sap and to 

 open these roads after heavy snows (fig. 43). 

 Tapping need not be delayed until the sap 

 season has arrived. Large crews do not have to 

 be hurriedly assembled to tap the trees and 

 hang the buckets. Instead, the lightweight plas- 

 tic tubing can be carried by hand through the 

 woods when convenient. 



Some setbacks were encountered when plas- 

 tic tubing was first introduced. Since it had 

 been emphasized that sap issues from the tree 

 under high pressure (,39), systems for installing 

 the pipelines were patterned after those used 

 for high-pressure waterlines. It was anticipated 

 that enough pressure was developed by the 

 tree to force the sap through the pipelines, but 

 this was not true. The sap leaks from the 

 tissues of the tree under a wide range of pres- 

 sures, from very low (almost immeasurable) to 

 as much as 40 pounds per square inch. The 

 pressure is affected by many factors, among 

 which are the temperatures of the air, tree 

 bark, and soil. In many runs, and often 

 throughout most of a run, sap leaks from the 

 tree under very low pressure. Thus, only a 

 slight obstruction in a pipeline provides suffi- 

 cient back pressure (resistance to flow) to equal 

 or exceed the pressure at which the sap is being 

 exuded from the tree. Hence, sap flow is pre- 

 vented. 



Causes for back pressures (obstructions) in 

 the line are (1) gas (vapor) locks resulting from 

 pockets of gas exuded from the tree along with 

 the sap (8) or from air pockets that result from 

 air that has leaked into the tubing around the 



different connections, especially at the spouts 

 (through the vent tubes); (2) low places in the 

 line where pockets of sap collect, and (3) ice 

 plugs of frozen sap. Of these three causes, 

 gaslocks are most frequent and may cause 

 enough back pressure to support a 5-foot col- 

 umn of sap. However, gaslocks can be kept to a 

 minimum by careful installation and by provid- 

 ing vents to free the trapped gases or air. 



The effect of ice in the pipelines is a contro- 

 versial subject. Many believe that by the time 

 the air temperature has risen sufficiently to 

 cause sap to flow from the tree, the tubing will 

 have warmed sufficiently to partly melt the ice 

 and allow passage of the sap. Others believe 

 that the elasticity of the tubing will permit the 

 sap to pass by the ice plug. This is unlikely. Still 

 others believe that tubing laid directly on the 

 ground, whether snow covered or not, will ab- 

 sorb enough latent heat from the earth to melt 

 the ice in the tubing before any appreciable 

 flow of sap occurs. Ice in tubing installed on the 

 ground often melts before ice in tubing sus- 

 pended in the air. (This can be observed when 

 the two systems are installed in the same sugar 

 grove.) There is almost complete agreement 

 that ice in tubing layered between two falls of 

 snow melts very slowly because of the insulat- 

 ing effect of the snow. The tubing must be 

 pulled up out of the snow before the ice will 



PN-4739 



Figure AS. — Tubing can be used for a small group of trees 

 in an inaccessible area or for roadside trees. 



